Oxidation number of cu in cu(so4)2.5H2O
In Cu(SO4)2.5H2O, the sulfate ion (SO4) has a charge of -2. There are two sulfates in the formula, so their total charge is -4. The water (H2O) molecules have no charge, so they don't affect the oxidation state of the copper ion.
To find the oxidation state of copper (Cu), we can use the fact that the overall charge of the compound is neutral (since there are no other ions mentioned). Therefore:
Charge on Copper + (-4) = 0
Charge on Copper = +4
So the oxidation state of copper in Cu(SO4)2.5H2O is +4.