The Law of Octaves and Newlands' Periodic Table Quiz

All three of them

Newlands

Chancourto

Dobereiner (correct)

Newly discovered elements did not fit into the law (correct)

In some cases, two elements were placed in the same slot

Unlike elements were grouped under the same slot

It was only applicable to elements with atomic masses up to 40

Only three triads could be identified from the elements known at the time

All of these

They were groups of three elements with similar properties (correct)

The atomic mass of the middle element was the arithmetic mean of the other two