The atomic number of an element E is 16. The number of electrons in its ion $E^{2-}$ will be:

Atomic number- 16-sulphur, valency (-2),

No. of protons= No of electrons =16

This balance is valid for a neutral atom. When it becomes an ion, clearly it has gained electrons by 2 in number, hence its current electron status is 16 + 2 = 18.

so $E^{2-}$ will be:18