Ionisation Energies MCQ's PDF

1. What is the de nition of the rst ionisation energy? a) The energy required to add one electron to a neutral atom in the gaseous state b) The energy required to remove one electron from one mole of gaseous atoms c) The energy required to remove one proton from one mol...

1. What is the de nition of the rst ionisation energy? a) The energy required to add one electron to a neutral atom in the gaseous state b) The energy required to remove one electron from one mole of gaseous atoms c) The energy required to remove one proton from one mole of gaseous atoms d) The energy required to add one neutron to one mole of gaseous atoms Answer: b) The energy required to remove one electron from one mole of gaseous atoms *Explanation: First ionisation energy is de ned as the energy required to remove one electron from one mole of gaseous atoms to form one mole of 1+ ions.* 2. What is the general trend in rst ionisation energy across a period? a) It decreases b) It remains constant c) It increases d) It uctuates randomly Answer: c) It increases *Explanation: Across a period, the nuclear charge increases while the shielding e ect remains constant, leading to a stronger attraction between the nucleus and the outer electron, thus increasing the ionisation energy required.* 3. What factor primarily determines the rst ionisation energy of an element? a) Atomic mass b) Number of neutrons c) Number of protons d) Distance from the nucleus to the outer electron Answer: d) Distance from the nucleus to the outer electron *Explanation: The distance from the nucleus and the electron shielding e ect primarily determine how much energy is required to remove the outer electron.* 4. Why does the rst ionisation energy decrease down a group? a) Increased nuclear charge b) Increased electron shielding and distance from nucleus c) Decreased atomic mass d) Decreased electronegativity Answer: b) Increased electron shielding and distance from nucleus *Explanation: Down a group, both electron shielding and atomic radius increase, reducing the nuclear attraction experienced by the outer electron.* 5. Which of the following equations represents the rst ionisation energy of Sodium? a) Na(g) → Na⁺(g) + e⁻ b) Na(g) + e⁻ → Na⁻(g) c) Na⁺(g) → Na²⁺(g) + e⁻ d) Na(g) → Na(g) + e⁻ Answer: a) Na(g) → Na⁺(g) + e⁻ *Explanation: This equation represents the removal of one electron from one mole of sodium atoms in the gaseous state forming sodium ions.* 6. What causes the large jump in ionisation energy when removing an electron from a noble gas con guration? a) Increased nuclear charge b) Increased inter-electronic repulsion c) Electron is being removed from a lower energy level d) Decreased atomic radius Answer: c) Electron is being removed from a lower energy level fi fl fi fi fi fi fi fi fi ff ff *Explanation: Removing an electron from a noble gas con guration means taking an electron from a stable, full energy level, causing a large increase in required energy.* 7. What is the rst ionisation energy in uenced by? a) Distance from the nucleus b) Nuclear charge c) Electron shielding d) All of the above Answer: d) All of the above *Explanation: The rst ionisation energy is in uenced by nuclear charge, electron shielding, and the distance of the outer electron from the nucleus.* 8. Which element has a higher rst ionisation energy, Magnesium or Aluminium? a) Magnesium b) Aluminium c) They have the same ionisation energy d) It varies with temperature Answer: a) Magnesium *Explanation: Magnesium has a higher rst ionisation energy because its outer electron is in an s orbital, which experiences less shielding compared to the p orbital of Aluminium.* 9. What is the general trend for successive ionisation energies of an element? a) They remain constant b) They decrease with each successive electron removed c) They increase with each successive electron removed d) They decrease and then increase Answer: c) They increase with each successive electron removed *Explanation: Successive ionisation energies increase because after the rst electron is removed, the remaining electrons experience a relatively higher nuclear charge making them harder to remove.* 10. Which of the following best explains the rst ionisation energy of sulfur being lower than that of phosphorus? a) Higher nuclear charge in sulfur b) Electron-electron repulsion in sulfur's p-orbital c) Sulfur has more protons d) Sulfur has larger atomic radius Answer: b) Electron-electron repulsion in sulfur's p-orbital *Explanation: Sulfur has paired electrons in one of its p-orbitals, causing repulsion and making it easier to remove one of those electrons compared to phosphorus with singly occupied p- orbitals.* 11. What is the relationship between the rst ionisation energies of elements in group 2 and group 3 of the periodic table? a) Group 2 elements have higher ionisation energies b) Group 3 elements have higher ionisation energies c) Group 2 and group 3 elements have identical ionisation energies d) It varies randomly Answer: a) Group 2 elements have higher ionisation energies *Explanation: Group 2 elements have their outer electron in an s-orbital which is closer to the nucleus and less shielded than group 3's p-orbital electrons, thus requiring more energy to remove.* 12. Which element would you expect to have the highest rst ionisation energy in Period 3? a) Sodium fi fi fi fl fi fi fl fi fi fi fi  b) Silicon c) Chlorine d) Argon Answer: d) Argon *Explanation: Argon, being a noble gas with a full outer shell, has the highest rst ionisation energy as it has a very stable electronic con guration.* 13. Why does the rst ionisation energy of Neon di er signi cantly from that of Sodium? a) Neon has more electron shells b) Sodium has a lower nuclear charge c) Neon has no electron shielding e ect d) The outer electron removed from Na has greater shielding between it and the nucleus Answer: d) The outer electron removed from Na has greater shielding between it and the nucleus *Explanation: Sodium is in the period below Ne. The electron in its outer shell has grater shielding from the nucleus, so is easier to remove.* 14. Which pair of successive ionisation energies shows the highest increase for a Group 1 element? a) 2nd and 3rd ionisation energies b) 3rd and 4th ionisation energies c) 1st and 2nd ionisation energies d) 10th and 11th ionisation energies Answer: c) 1st and 2nd ionisation energies *Explanation: The biggest increase often occurs between the 1st and 2nd ionisation energies because the rst removes the outermost electron and the second typically removes from a stable noble gas con guration.* 16. Which of the following elements would exhibit large jumps in successive ionisation energies after the removal of the rst three electrons? a) Sodium b) Magnesium c) Carbon d) Boron Answer: d) Boron *Explanation: Boron has a signi cant increase in successive ionisation energies after removing the rst three electrons because the subsequent removal involves breaking into a more stable inner shell con guration.* 17. Which of these elements has the lowest rst ionisation energy? a) Fluorine b) Chlorine c) Bromine d) Iodine Answer: d) Iodine *Explanation: Down the group, the atomic radius increases and the outer electrons are more shielded from the nucleus, thus Iodine has the lowest rst ionisation energy among the given options.* 18. What contributes to the increase in rst ionisation energy across a period? a) Decrease in atomic mass b) Increase in electron-electron repulsion c) Decrease in nuclear charge d) Increase in e ective nuclear charge fi fi fi fi ff fi fi fi ff fi fi fi ff fi fi fi  Answer: d) Increase in e ective nuclear charge *Explanation: Across a period, the nuclear charge increases due to more protons while shielding remains nearly constant, thus increasing the e ective nuclear charge which attracts the outer electrons more strongly.* 19. Why is the second ionisation energy of Sodium higher than its rst ionisation energy? a) The second electron is removed from a neutral atom b) The second electron is removed from a stable ion c) The second electron is closer to the nucleus and experiences less shielding d) Electron repulsion makes it easier to remove the second electron Answer: c) The second electron is closer to the nucleus and experiences less shielding *Explanation: The second ionisation energy of Sodium is higher because the electron removed is from a lower energy level which is closer to the nucleus and less shielded.* 20. Which of these elements has the highest second ionisation energy? a) Lithium b) Beryllium c) Boron d) Carbon Answer: a) Lithium *Explanation: Lithium has the highest second ionisation energy because after removing the rst electron, the second removal involves an electron from a stable full shell con guration.* 21. Why is there a large jump between the rst and second ionisation energies of an alkali metal? a) The rst electron is easier to remove b) Removing the rst electron creates a noble gas con guration c) Electron shielding increases after the rst electron d) Remaining electrons experience decreased nuclear charge Answer: b) Removing the rst electron creates a noble gas con guration *Explanation: Alkali metals achieve a stable noble gas con guration after losing one electron, making the subsequent removal of a second electron signi cantly harder.* 22. Which period 2 element has the highest rst ionisation energy? a) Beryllium b) Carbon c) Nitrogen d) Neon Answer: d) Neon *Explanation: Neon has the highest rst ionisation energy among period 2 elements due to its stable octet con guration.* 23. Why does the rst ionisation energy decrease from magnesium to aluminium? a) Increase in atomic radius b) Increase in nuclear charge c) Electron removed from a higher energy p-orbital d) Decrease in shielding e ect Answer: c) Electron removed from a higher energy p-orbital *Explanation: The electron removed from aluminium comes from a higher energy p-orbital which is easier to remove than an electron from a lower energy s-orbital in magnesium.* 24. Which element will have a larger di erence between its rst and second ionisation energies: Calcium or Potassium? a) Calcium b) Potassium c) They have the same di erence fi fi fi fi ff ff ff fi fi ff fi fi fi ff fi fi fi fi fi fi fi fi  d) It varies with conditions Answer: b) Potassium *Explanation: Potassium will have a larger di erence because the rst ionisation removes one electron to achieve noble gas con guration, making the removal of a second electron signi cantly harder.* 25. How do successive ionisation energies vary for sodium? a) They decrease gradually b) They remain constant c) The rst is lowest and then they increase with large jumps at noble gas con gurations d) They increase and then decrease randomly Answer: c) The rst is lowest and then they increase with large jumps at noble gas con gurations *Explanation: After the rst electron is removed from sodium, the successive removal of electrons increases in energy particularly after achieving a noble gas like stable con guration.* 26. Which transition involves the largest increase in ionisation energy for oxygen? a) 1st to 2nd b) 2nd to 3rd c) 3rd to 4th d) 5th to 6th Answer: d) 5th to 6th *Explanation: The largest increase in ionisation energy for oxygen occurs when removing electrons that breaks into the stable noble gas con guration after the removal of the fth electron.* 27. Why does the rst ionisation energy of lithium di er signi cantly from that of beryllium? a) Lithium has a higher nuclear charge b) Beryllium has a higher electron shielding e ect c) Beryllium has a stable lled s-orbital d) Lithium has more protons Answer: c) Beryllium has a stable lled s-orbital *Explanation: Beryllium has a lled s-orbital which requires more energy to remove an electron from a stable con guration compared to lithium.* 28. Which has the highest rst ionisation energy: Sodium (Na) or Potassium (K)? a) Sodium b) Potassium c) They have the same ionisation energy d) It changes with conditions Answer: a) Sodium *Explanation: Sodium has a higher rst ionisation energy because potassium’s outer electron is further from the nucleus and more shielded, making it easier to remove.* 29. What is the general trend in ionisation energies down a group? a) They increase b) They decrease c) They remain unchanged d) They vary irregularly Answer: b) They decrease *Explanation: Down a group, the atomic radius increases and electrons are more shielded from the nucleus, making it easier to remove the outermost electron.* 30. Which concept explains the increase in ionisation energy within a period but a decrease down a group? a) E ective nuclear charge ff fi fi fi fi fi fi fi fi fi fi fi fi ff ff ff fi fi fi fi fi fi fi b) Electron A nity c) Atomic mass number d) Number of isotopes Answer: a) E ective nuclear charge *Explanation: The e ective nuclear charge increases across a period resulting in higher ionisation energies but decreases down a group hence decreasing ionisation energies.* ff ffi ff