Question

Why is copper (i) sulfate Cu2So4^-2? not copper (ii)?

Answer 1

copper (I) oxidation state is 1 Cu2So4
copper (II) oxidation state is +2 CuSo4
copper (i) also give up one electron so you need two of them to react with the sulfate ion (which has charge of -2)
and also all metallic ions have an multiple oxidation levels corresponding to the number of electrons they can exchange or loose
Hope this helps

Answer 2

Answer

This is because Copper (I) has +1 charge and Copper (II) has +2 charge.

Explanation

The chemical formula of an ionic compound consists of cation first, followed by anion. Both cations and anions are incolved to make compound to be nutral or charge entity for example Cu2SO4 is cuprous compound contain Cu (I) where two Cu give only one electron as  

Cu is cation and SO4 is anion

SO4 has a valency of -2

So, Cu2 has a valency of +2

But in Cu (II), The single copper gives two electron to SO4 and form CuSO4 compound named as copper sulphate.

These metalls are called transition metals who can change their oxidation states