Question

The valency of nitrate ion is ​

Answer 1

Nitrate ion (NO3) has one Nitrogen and three Oxygen atoms.

Oxygen lies in group 16 and thus has a valency of -2.

Nitrogen lies in the group 15 and has a charge of +5 forming the bond with three oxygen atoms.

5 – 3*(2) = -1

So if you add the valency of all the atoms, you get the answer as -1.