Question

How to find valency of an element in a compound?

Answer 1

We can find the valency of an element in a compound when we know the valency of first element.

like if we have to find valency of sulphate in the compound calcium sulphate

then,we have to write formula
CaSO4

as we know the valency of calcium​ is +2

here by criss-cross method,
the valency of sulphate we get -2.