An element A forms a compound AH3 with hydrogen. Another element B forms a compound BA2 with B. Given that the valency of hydrogen is 1, what are the valencies of A & B?

A - 3

B - 6

Explanation:

The valency of hydrogen atom is + 1

The valancy of an atom of other element combining with the hydrogen atom can be determined from the number of associated hydrogen.

when H combines with A, three atoms of hydrogen are used. Thus the valency of element A is - 3

Now B combines with two molecules of A whose valency is - 3

The valency of B would be twice the valency of element A i. e 6

if hydrogen combines with B, then the compound formed will be BH6