Question

The electronic configuration of an element B is 2, 8, 7 and it forms an ionic compound AB2
with another element A. What is the valency of element A?

Answer 1

the valency of A is 2

valency of B = 1
and the formula = AB2

we know during writing fornulas the valency gets interchanged

therefore valency of A = 2

Answer 2

It is clear that the valency of B is 1

The compound is AB2

While we write the formula, Valency of A goes to B and that of B to A.

Thus, Valency of A is 2

As metals are placed before in formula, Valency of A is +2