Class 8 Coal and Petroleum Important Questions - Science Paper PDF

Class 8 Chapter 5 - Coal and Petroleum Important Questions with Answers Q1: You are provided with a mixture of petroleum and water. Can you suggest a method to separate the two? Answer: Petroleum has a lower density than water. The procedure of decantation can be used to separate the two. Since it...

Class 8 Chapter 5 - Coal and Petroleum Important Questions with Answers Q1: You are provided with a mixture of petroleum and water. Can you suggest a method to separate the two? Answer: Petroleum has a lower density than water. The procedure of decantation can be used to separate the two. Since it floats on top of the water, light petroleum can be precisely poured. Thus, using this method, we can easily separate the two. Q2: What does CNG stand for and why is it considered to be a better fuel than petrol? Answer: CNG stands for compressed natural gas, and it is a better fuel than gasoline because it is an environmentally friendly gas that does not hurt the environment. In addition, it emits substantially less smoke. Its principal application is as a fuel substitute in automobiles. It emits fewer greenhouse gases than other countries (in comparison with LPG). Methane is the most essential element of CNG. Since it disperses rapidly into the air, it is relatively safe. As the crankcase oil does not dilute and pollute, it increases the life of the lubricating oil. It is very healthful because it easily disperses into the air. Q3: Name the petroleum product used as fuel for stoves, lamps and jet aircrafts. Answer: Kerosene is a petroleum-based substance. It's used to power lamps, stoves, and jet planes. Kerosene is a crude oil fraction made up of the carbon atoms C12H26–C15H32. Kerosene is a fossil fuel that is produced as a by-product of crude oil. Energy is stored in the form of chemical energy in fossil fuels, which is turned into heat and light energy when burned. Kerosene is often pale yellow or colourless in appearance, with a pleasant odour. It can also be used as a cleaning agent and for heating and cooking. Q4: Fill in the blanks in the following sentences. (a) Coal is one of the _________ used to cook food. (b) When heated in air, coal burns and produces mainly _______ gas. (c) Coal tar is a black, thick ________ with an ________ smell. (d) Petroleum, _________ and _________ are fossil fuels. (e) Forests and coal are ___________ natural resources. Answer: (a) Coal is one of the fuels used to cook food. (b) When heated in air, coal burns and produces mainly Carbon dioxide gas. (c) Coal tar is a black, thick liquid with an unpleasant smell. (d) Petroleum, coal and natural gas are fossil fuels. (e) Forests and coal are exhaustible natural resources. Q5: The underlined words in the following sentences have been jumbled up. Write them in their correct form. (a) Loca is obtained from mines. (b) Umpetlore is a fossil fuel. (c) Rineryfe is a place where various fractions of petroleum are separated. (d) Keenrose is a fuel used in )et crafts. (e) Nutsgilh s an example of inexhaustible natural resources. Answer: (a) Coal is obtained from mines. (b) Petroleum is a fossil fuel. (c) Refinery is a place where various fractions of petroleum are separated. (d) Kerosene is a fuel used in jet crafts. (e) Sunlight is an example of inexhaustible natural resources. Q6: Fill in the blanks. (a) The slow process of conversion of dead vegetation into coal is called _________. (b) Coal and petroleum are formed from the dead remains of organisms and are known as ___________. (c) The black thick liquid with _________ smell is known as coal tar. (d) During the processing of coal to get coke, coal tar and ________ are also obtained. (e) The process of separating the various constituents of petroleum is known as _________. (f) Excessive burning of fossil fuels is a major cause of ___________. Answer: (a) The slow conversion of dead vegetation into coal is called carbonisation. (b) Coal and petroleum are formed from the dead remains of organisms and are known as fossil fuels. (c) The black, thick liquid with an unpleasant smell is known as coal tar. (d) During the processing of coal to get coke, coal tar and coal gas are also obtained. (e) The process of separating the various constituents of petroleum is known as Fractional Distillation. (f) Excessive burning of fossil fuels is a major cause of Global Warming. Q7: Write True/False against the following statements. (a) Oxygen in air is an exhaustible natural resource. (b) Resources which are present in unlimited quantity in nature are called exhaustible natural resources. (c) Wildlife is an exhaustible natural resource. (d) Under high temperature and pressure, dead plants get slowly converted to coal. (e) CNG is less polluting fuel than petrol and diesel. Answer: (a) False. Because oxygen can be reused, oxygen in the air is an inexhaustible natural resource. (b) False. Resources which are present in unlimited quantity in nature are termed inexhaustible natural resources. (c) True. Wildlife is an exhaustible natural resource. (d) True. Under high temperature and pressure, dead plants get slowly converted to coal. (e) True. CNG is less polluting fuel than petrol and diesel. Short Answer Type Questions Q1: Sunlight and air are inexhaustible natural resources. Comment. Answer: Natural resources which are inexhaustible are those whose quantity is not based on consumption or is not subject to scarcity. The amount of sunlight and air available is unaffected by human consumption. This is why these natural resources are inexhaustible. Q2: Some natural resources are given in a box. Classify them into the exhaustible and inexhaustible natural resources. air, coal, natural gas, sunlight, petroleum, minerals, forests, oxygen. Answer: Exhaustible resources are coal, natural gas, petroleum, minerals, forests. They are in limited supply and are being depleted by human activity. These resources can't be replenished once they've been depleted. Non-renewable or non-replenishable resources are those that cannot be replenished. They, like iron and coal, require conservation measures to ensure that they can be used in the future. Inexhaustible resources are air, sunlight, oxygen. They exist in an infinite supply and cannot be depleted by human activity. These resources have the power to regenerate themselves over time. These are resources that can be replenished or are renewable. They do not require conservation measures because they can be renewed, such as sunlight and water. Q3: Write two important uses of coke. Answer: Coke is a high-carbon substance made by distilling coal in a destructive manner. Coke is mostly used as a fuel for stoves, furnaces, and blacksmithing. Because coke creates very little smoke, it is sometimes preferred over coal. It is also utilised to produce iron in a blast furnace. Steel and a variety of other products are made from coke. It is used as a reducing agent in the process of metal extraction. Zinc and iron, for example. Q4: Write the characteristics and some important uses of coal. Answer: Coal is a black, stone-like substance. It's one of the fuels used in the kitchen. It was once employed in railway engines to generate steam to power them. It is used as a fuel in thermal power plants, as well as in a variety of other sectors. Coal is one of the fossil fuels. It's a brittle and flammable fuel. It has a lot of carbon in it. It is an energy source. The important uses of coal are as follows- It is used to generate energy and as a cooking fuel in households. It's used to make coal gas and coke. Coal is also used in the manufacture of specialised products including activated carbons, carbon fibre, and silicon metals. Q5: Look at Fig. 5.1 where petroleum and natural gas deposits are shown. Why do we find oil layer above water layer? Answer: The oil layer is found above the water layer because oil is light and floats over it. Furthermore, because oil has a lower density than water, it floats on the water's surface. Q6: Fill in the blanks and complete the story. About 300 million years ago the earth had dense _________ in low lying wetland areas. Due to natural processes, like __________, these forests got buried under the ________. As more ________ deposited over them, they were compressed. The __________ also rose as they sank deeper and deeper. Under high _________ and high _________, dead plants got slowly converted into coal. Answer: About 300 million years ago, the earth had dense forests in low-lying wetland areas. Due to natural processes, like floods, these forests got buried under the earth surface. As more soil deposited over them, they were compressed. The pressure also rose as they sank deeper and deeper. Under high temperature and high pressure, dead plants got slowly converted into coal. Q7: Match the items given in Column I with the items of Column II. Column I Column II (a) Used for road (i) Black gold surfacing (ii) Vaseline and (b) Natural gas candles (c) Petroleum (iii) Bitumen (d) Paraffin wax (iv) CNG Answer: (a) Used for road surfacing - (iii) Bitumen (b) Natural gas - (iv) CNG (c) Petroleum - (i) Black gold (d) Paraffin wax - (ii) Vaseline and candles Long Answer Type Questions Q1: Name the products obtained and their uses when coal is processed in industry. Answer: During coal processing, the following items are produced: Coal tar is used to make synthetic pharmaceuticals, explosives, fragrances, paints, and plastics, among other things. Coke is a substance that is used to make steel and extract metals. Coal gas is a fuel that is used in industry. Q2: We say fossil fuels will last only for a few hundred years. Comment. Answer: The creation of fossil fuels takes a very long time. It also requires special circumstances, which aren't common. As a result, their limited supply will only endure a few hundred years. Fossil fuels are exhaustible resources. Nature has a limited supply of these resources. Human activities have the potential to deplete them. Forests, wildlife, minerals, coal, petroleum, natural gas, and other resources are examples of these resources. Petroleum and coal are both fossil fuels. It took millions of years for dead organisms to be turned into these fuels. The known reserves of these, on the other hand, will last only a few hundred years. Furthermore, the burning of these fuels contributes significantly to air pollution. Their use contributes to global warming. As a result, we should only use these fuels when absolutely required. As a result, the environment will be improved, the risk of global warming will be reduced, and they will be available for a longer length of time. Q3: We read in newspapers that burning of fuels is a major cause of global warming. Explain why. Answer: The use of fossil fuels in many regions has resulted in significant air pollution. Sulphur dioxide, carbon dioxide, and other hazardous gases are produced when fossil fuels are burned. The gases that vehicles, power plants, companies, residences, and other sources of pollution produce assist to raise the temperature of the environment and the earth by heating the atmosphere and air. Q4: While driving what are the tips we must follow to save petrol/diesel/natural gas? Answer: Natural gas generates much lesser nitrogen oxides (NOx) and particulate matter (PM) when burned than diesel or even gasoline. In addition, the combustion process is quieter. However, there is a more compelling reason to conserve fossil fuels, to contribute in environmental recovery. 1. Make sure the tyre pressure is correct. 2. Maintain the vehicle on a regular basis. 3. Maintain a consistent and moderate speed to save fuel waste. 4. At traffic signals or other places where you have to wait, turn off the motor. 5. When at all possible, avoid using the air conditioner. Air conditioners consume 10% more energy. 6. Replace the lubricant on a regular basis. Only use branded oil that has been suggested by the manufacturer. Q5: Imagine that all the exhaustible natural resources are exhausted by human activities. Do you think survival of living beings would be possible? If yes, why?, If not, why not? Answer: It would be impossible for humans to survive if natural resources were not available. Fossil fuels are necessary for human survival. After oxygen, it is one of the most crucial factors in our lives. Fossil fuels are used to generate energy, which is used to power factories and provide all of the other necessities without which a human would perish. Apart from these, humans use fossil fuels to power their automobiles. Human life will come to a halt without fuel. For example, forests are a significant natural resource that produces rain, prevents soil erosion, and floods, and provides oxygen and other valuable items. We can't picture what life would be like without them. Fossil fuels, wildlife, forests, minerals, and other non-renewable natural resources are all important in our lives. Q6: Why petrol is exhaustible natural resource, whereas sunlight is not? Explain. Answer: Petrol is a fossil fuel created by the breakdown of dead plants and animals inside the waters over millions of years. It can only be found in a handful of locations. This fossil fuel is converted into petrol, which is a precious commodity. Humans use it more ferociously the more restricted it is. Because of this, petrol is a finite resource. Sunlight, on the other hand, is a type of energy that the sun generates. A lot of energy is generated in this process. And will carry on indefinitely, as long as the inhabitants of the Earth exist. Q7: Write some important uses of the various constituents of petroleum. Answer: Petroleum has been used in some capacity. Petroleum is made up of sea-based creatures. As these organisms perished, their remains sank to the ocean's bottom, where they were buried in layers of sand and clay. Absence of air, high temperature, and high pressure turned dead organisms into petroleum and natural gas over millions of years. It has a variety of applications, including: Agriculture Detergents, Dyes, and Others Plastics, Paints and More Pharmaceuticals Rubber Constituents of petroleum Uses Petroleum Gas in Liquid Fuel for home and industry form (LPG) Motor fuel, aviation fuel, solvent Petrol for dry cleaning Fuel for stoves, lamps and for jet Kerosene aircrafts Fuel for heavy motor vehicles, Diesel electric generators Lubricating oil Lubrication Paraffin wax Ointments, candles, Vaseline etc. Bitumen Paints, road surfacing Q8: Coal reserves are said to be enough to last for another hundred years. Do you think we need to worry in such case? Why or why not? Answer: Coal deposits are quite limited. A coal reserve is only good for about 100 years. Given the rate at which humans consume coal, it's unlikely that it will survive another 100 years. The consumption of coal is steadily increasing. Coal is used extensively in everything from modest homes to large companies and power plants. As a result, coal is becoming scarce. This fossil fuel inside the earth takes millions of years to return to nature. However, the consumption is excessive, and it will not last long. As a result, we should use coal with caution and responsibility. Apart from that, we should make use of other renewable energy sources. Q9: What steps would you suggest for the judicious use of fossil fuels? Answer: Because fossil fuels are limited and only exist in small quantities in nature, they should be used with caution. Furthermore, fossil fuels take millions of years to produce. When fossil fuels are burned, pollution results. Steps made to ensure that fossil fuels are used wisely: Make more use of public transportation.  Don't throw your fossil fuels. While driving to school or work, we should consider carpooling. Renewable energy sources such as wind and solar power are being adopted. Instead of LPG, biogas is used as a fuel. Maintain the vehicle on a regular basis. At traffic signals or other places where you must wait, turn off the motor. Q10: Complete the crossword Fig. 5.2 with the help of the clues: Across 1. Fuels obtained from dead remains of living organisms. (6,5) 2. A process by which the various constituents of petroleum are separated. (8) 3. A porous black substance obtained from coal. (4) 4. Another name for motor fuel. (6) Down 5. The substance obtained by carbonisation. (4) 6. Fuel for heavy motor vehicles. (6) 7. A petroleum product used for road surfacing. (7) 8. Dead remains of sea animals got converted into it. (9) Answer: Across 1. FOSSIL FUELS 2. REFINING 3. COKE 4. PETROL Down 5. COAL 6. DIESEL 7. BITUMEN 8. PETROLEUM CBSE Class 8 Science Chapter 5 MCQ Type Questions 1. From the given statements, choose the incorrect one. (a) Petroleum gas in liquid form (LPG) is used as fuel in homes and industries (b) Kerosene is used as fuel for stoves, lamps and jet aircraft (c) Diesel is used as fuel for heavy motor vehicles, electric generators (d) Paraffin is used in paints and road surfacing Answer: (a) Petroleum gas in liquid form (LPG) is used as fuel in homes and industries. 2. Naphthalene obtained from coal tar is used as _______ (a) Honey bee repellant (b) Mosquito repellant (c) Snake repellant (d) Moth repellant Answer: (d) Moth repellant 3. Name a pair of exhaustible Natural resources from the following: (a) Air and sunlight (b) Coal and soil (c) Water and petroleum (d) Minerals and wildlife Answer: (d) Minerals and wildlife 1. Why is it important to conserve forests? 2. Mention any one action that you have undertaken to conserve trees. 3. State whether the following statements are True or False. Correct the false statements. o (i} There can be a wildlife sanctuary within a biosphere reserve. o (ii} Plants of a particular area are collectively termed as fauna. o (iii} Deforestation leads to an increase in the water holding capacity of the soil. o (iv} Bison is an endemic fauna of Pachmarhi Biosphere Reserve. 4. Can a forest reqenerate naturally in a short period of time? 5. Name the first Reserve Forest of India. Short Answer Type Questions 1. Why are wildlife sanctuaries important for conservation of plants and animals? 2. Why are endemic organisms ir greater danger of becoming extinct? 3. How are even small animals important in an ecosystem? 4. A new species Xis introduced n a forest. How is it likely to affect the local species of that area? 5. Ooes soil erosion affect the fertility of soil? How? 6. What is the unique feature of the biodiversity found in Panchmarhi Biosphere Reserve? 7. Mention the aim of Forest (Conservation} Act. 8. What is biodiversity? Long Answer Type Questions 1. Is deforestation associated with global warming? Explain. 2. How does deforestation lead to frequent floods and droughts? 3. Why should we save paper? Class 8 Chapter 6 - Combustion and Flame Important Questions with Answers Q1: Boojho wants to separate the following materials as combustible and non-combustible. Can you help him? Charcoal, chalk, stone, iron rod, copper coin, straw, cardboard, glass, paper, candle, wood. Answer: Combustible substances — charcoal, straw, card board, paper, candle wood. Non-combustible substances — chalk, stone, iron rod, copper coin, glass. Combustible substances are those that can be ignited or burned. For example, paper, fabric, cooking gas (LPG), compressed natural gas (CNG), kerosene oil, wood, charcoal, and so on. Non-combustible substances are those that do not ignite. Stone, cement, bricks, soil, sand, water, iron nails, and so on. Q2: Indicate whether the following statements are True or False. Also write the false statements in their correct form. (a) Air is necessary for combustion. (b) Magnesium is a non-combustible metal. (c) Carbon dioxide is an excellent fire extinguisher. (d) Calorific value of wood is higher than that of coal. Answer: (a) True. Air is necessary for combustion. (b) False. Magnesium is a combustible metal. (c) True. Carbon dioxide is an excellent fire extinguisher. (d) False. Calorific value of coal is higher than that of wood. Q3: Match the Items of Column A with the items of Column B. Column A Column B (a) Oxides of sulphur (i) fire extinguisher and nitrogen (ii) incomplete (b) CNG combustion of coal (iii) very low ignition (c) Oxygen temperature (d) inflammable substance (iv) acid rain (v) necessary for (e) carbon dioxide combustion (f) carbon monoxide (vi) fuel for automobiles Answer: (a) Oxides of sulphur and nitrogen - acid rain (b) CNG - fuel for automobiles (c) Oxygen - necessary for combustion (d) Inflammable substance - very low ignition temperature (e) Carbon dioxide - fire extinguisher (f) Carbon monoxide - incomplete combustion of coal Q4: Match the following for the flame of a candle. Column A Column B Column C (i) innermost zone of (a) hottest part (x) blue unburnt wax vapours (ii) middle zone of partial (b) moderately hot (y) black combustion (iii) outer zone of (c) least hot (z) yellow complete combustion Answer: (a) hottest part - outer zone of complete combustion - blue (b) moderately hot - middle zone of partial combustion - yellow (c) least hot - innermost zone of unburnt wax vapours - black Q5: If you hold a piece of iron wire with a pair of tongs inside a candle flame or a Bunsen burner flame, what will you observe? Will it produce a flame? Answer: The iron wire glows and turns red. It does not emit a flame. Because metals have a high ignition temperature and are good heat conductors, most atoms in a solid chunk of metal do not have access to oxygen atoms. As a result, metals do not burn effectively in prevalent conditions. As the iron heats up enough to melt slightly, it flashes a dazzling yellow-orange colour and emits a shower of sparks. Q6: Fill in the blanks using the words given in the box. ignition, petrol, combustion, calorific value, combustible, inflammable (a) A chemical process in which a substance reacts with oxygen to give off heat is called _______. (b) Wood, paper, CNG are ________ substances. (c) The lowest temperature at which a substance catches fire is called its _________ temperature. (d) Ignition temperature of ________ is lower than that of wood. (e) The substances which have very low __________ temperature and can easily catch fire with a flame are called _____________ substances. (f) The amount of heat energy produced on complete combustion of lkg of a fuel is called its _________. Answer: a) combustion b) combustible c) ignition d) petrol e) ignition, inflammable f) calorific value Q7: People usually keep Angethi/burning coal in their closed rooms during winter season. Why is it advised to keep the door open? Answer: Many hazardous gases are produced when angethi is burned, including carbon dioxide and carbon monoxide. The flow of oxygen is likewise reduced which creates breathing difficulties and can even kill someone who is sleeping. As a result, it is recommended that the door be left open to allow for proper air and oxygen movement. Angithis are typically used to create heat from burning coal and have glowing coal or charcoal bits but little or no flames when in use. Coal-burning energy plants are a main cause of air pollution and greenhouse gas emissions. Coal combustion emits sulphur dioxide, a hazardous chemical associated with acid rain, in addition to carbon monoxide and heavy metals like mercury. Q8: Write True/False against the following statements and also correct the false statement. (a) A physical process In which a substance reacts with oxygen to give off heat is called combos ion. (b) Water is the best extinguisher for fires involving electrical equipment. (c) Alcohol, CNG and LPG are inflammable substances. (d) Increased concentration of nitrogen in air is believed to cause global warming. (e) Greater the calorific value, better is the fuel. (f) Middle zone is the hottest zone of a flame. (g) The substances which vaporise during burning, give flame. Answer: (a) False A chemical process in which a substance reacts with oxygen to give off heat is called combustion. (b) False Carbon dioxide is the best extinguisher for fires involving electrical equipment. (c) True Alcohol, CNG and LPG are inflammable substances. (d) False Increased concentration of carbon dioxide in air is believed to cause global warming. (e) True Greater the calorific value, better is the fuel. (f) False Outer zone is the hottest zone of a flame. (g) True The substances which vapourise during burning, give flame. Q9: Cracker on ignition produces sound. Why? Answer: When crackers are lit, they emit sound, heat, and light. An explosion is the term for this procedure. An explosion is a chemical reaction that occurs when a mixture of gases is present. An explosion occurs when a quick reaction occurs with the release of heat and light and the evolution of a big amount of gas. Chemical change can be seen in the explosion of fireworks. Substances are transformed into new ones during a chemical reaction. In other words, the substance's makeup changes. Unfortunately, most explosions are extremely dangerous and should only be performed by professionals. Some basic explosions, on the other hand, can be replicated and viewed on a far smaller scale. Q10: What do you understand by fuel efficiency? Answer: The quantity of energy produced when 1 kilogram of complete fuel is burned is referred to as fuel efficiency. The caloric value determines this. This is measured in kJ/kg. Long Answer Type Questions Q1: You are provided with three watch glasses containing milk, petrol and mustard oil, respectively. Suppose you bring a burning candle near these materials one by one, which material(s) pull catch fire instantly and why? Answer: Because petrol is highly flammable, it will catch fire instantly. The ignition temperature of mustard oil and milk is extremely high. As a result, they will not catch fire right away. Petrol is very volatile, which means it produces vapour even at low temperatures. As a result, it's more combustible. The lesser the volatility, and hence the flammability, the higher the chaining in the chemical composition. Because kerosene is a petroleum product, its ignition temperature is lower than that of other chemicals. The ignition point is also known as the ignition temperature. The lowest temperature to which a fuel must be heated in order to catch fire and begin burning is known as the ignition temperature of fuel. Q2: Manu was heating oil to fry potato chips. The cooking oil all of a sudden caught fire; he poured water to extinguish the fire. Do you think this action was suitable? If yes, why? If not, why not? In such a condition what should Manu have done? Answer: No. Because water is ineffective in fighting oil-based fires. Water has a lower density than oil. When water is poured over burning oil, it settles to the bottom of the container. However, because they reduce the flow of air, pouring dirt or sand may help to put out the fire. The particles will block the passage of air through the oil, putting an end to the fire. Because the oxygen supply is cut off, this occurs. Fire cannot be lit without the presence of oxygen. Manu should've turned the stove off and covered the frying pan with a lid. The flame would extinguish as a result of the interaction between the fuel and the oxygen. Q3: What are the three essential requirements to produce fire? How fire extinguisher is useful for controlling the fire? Answer: The following are the necessary components for producing fire: (i) Fuel: This is used to start a fire. (ii) Air: The most important factor in allowing the fire to burn. (iii) Heat: This is used to maintain the ignition temperature. The carbon dioxide in the fire extinguisher helps to limit the flow of air between the fuel and the air. Because CO2 is heavier than oxygen, it falls between the air and oxygen, helping in the control of the fire. It reduces the temperature of all burning substances to below the ignition temperature. It removes the burning substance's supporter, oxygen, from the flammable substance. Q4: Give two examples each for a solid, liquid and gaseous fuel along with some important uses. Answer: For Solid Coal and wood are options for solid fuels. Coal is primarily utilised in factories and enterprises, whereas wood is primarily used in residences. For Liquid Liquid Petrol, for example, is an example of liquid fuel. Kerosene is primarily used to cook meals in stoves, whereas petrol is used in automobiles. For Gases CNG and LPG are both considered gaseous fuels. Vehicles run by compressed natural gas (CNG). LPG is used in both vehicles and residences. Q5: The calorific values of petrol and CNG are 45000 kJ/kg and 50,000 kJ/kg, respectively. If you have vehicle which can run on petrol as well as CNG, which fuel will you prefer and why? Answer: Compressed natural gas has a higher calorific value than petrol. As a result, CNG will be a suitable choice. In addition, it generates more heat energy than petrol. It emits fewer pollutants and is less expensive than petrol. Compressed natural gas has a higher calorific value than petrol. As a result, CNG will be a suitable choice. In addition, it generates more heat energy than petrol. It emits fewer pollutants and is less expensive than petrol. Q6: Although wood has a very high calorific value, we still discourage its use as a fuel. Explain. Answer: Wood is not a preferred fuel for the following reasons: (i) It has a high ignition temperature, making it difficult to start a fire in wood. (ii) Burning wood emits a variety of hazardous gases, including carbon monoxide and carbon dioxide. These gases are poisonous and pollute the air. (iii) We would have to cut down trees to utilise wood as a fuel. Because trees are so essential to living things, cutting them down is discouraged. Q7: Forest fire produces a lot of air pollution. Write in brief about the reasons of forest fires. Answer: Consider the following factors: (i) When the grass in the forest becomes extremely dry, high temperatures encourage it to ignite, resulting in a forest fire. (ii) Lightning from the sky is another possibility. (iii) When villagers use fire to scare away animals, the dry grass burns, resulting in a forest fire. (iv) Friction between bamboos generates heat, which causes the bamboo to burn, causing a forest fire. Q8: Complete the crossword Fig. 6.1 with the help of the clues: Across 1. Non-metal which catches fire if exposed to air. (10) 3. The lowest temperature at which a substance catches fire is called its __________ temperature. (8) 5. The most common fire extinguisher. (5) Down 2. A chemical process in which a substance reacts with oxygen to give off heat. (10) 3. Petrol is used as a ____________ in automobiles. (4) 6. It is as hard as stone and black in colour. (4) Answer: Across 1. PHOSPHOROUS 3. IGNITION 5. WATER Down 2. COMBUSTION 3. FUEL 6. COAL CBSE Class 8 Science Chapter 6 MCQ Type Questions 1. Which among the following is a fuel? (a) Solid, Liquid or gas (b) Gas only (c) Liquid only (d) Solid only Answer: (a) Solid, Liquid or gas 2. What type of reaction is a combustion? (a) exothermic (b) endothermic (c) volatile (d) None of these Answer: (a) exothermic 3. Large scale cutting down of trees could result in ___ (a) afforestation (b) deforestation (c) both afforestation and deforestation (d) reforestation Answer: (b) deforestation 4. What is burning of LPG an example of? (a) spontaneous combustion (b) slow combustion (c) rapid combustion (d) both slow and spontaneous combustion Answer: (c) rapid combustion