Question

Why it is not possible to store cuso4 solution in zinc vessel?

Answer 1

Because Zinc would easily displace Copper from it's solution.

Zn + CuSO4-----------> ZnSO4  +  Cu

Answer 2

Zinc is more reactive than copper there fore zinc can displace copper  from its salt solution if copper sulphate solution is stored in a zinc vessel then zinc will displace copper from copper sulphate solution 
Zn+CuSo4=Cu+ZnSo4
ZnSo4 is very poisonous when reacted with copper sulphate.
so we cannot store copper sulphate in zinc vessel.