Name the scientists who gave the following laws in the early classification of elements:

(a) Law of octaves

(b) Law of triads

Name the Russian chemist who said that the properties of elements are a periodic functions of their atomic masses.

Rewrite the following statements after correction, if necessary:

(a) Group have elements with consecutive atomic numbers.

(b) Periodic are the horizontal rows of elements.

(c) Isotopes are the elements of the same group.

A, B and C are the elements of a Dobereiner’s triad. If the atomic mass of A is 7 and that of C is 39, what should be the atomic mass of B?

X and Y are the two elements having similar properties which obey Newland’s law of octaves. How many elements are there in-between X and Y ?