Question

what happens if a drop of water is poured over anhydrous copper sulphate

Answer 1

CuSO4.5H2O(s)⇌ CuSO4(s) + 5H2O(l)
it is an endothermic reaction

Answer 2

Copper sulphate is Cu SO₄ is a salt of copper.

The anhydrous copper sulphate without any moist or water molecules in it - is a light greenish white powder.  When a water drop falls on the anhydrous powder, water molecules are absorbed by the sulphate.

The pentahydrate form CuSO₄ . 5 H₂O    of copper sulphate is a beautiful bright shining blue crystalline solid.

Copper sulphate exists in various degrees of hydration ie., different number of molecules of water associated with one molecule of copper sulphate: like trihydrate and heptahydrate - which is green.

Cu SO₄  dissolves in a lot of water (not just drops) giving out heat, and forms [ Cu (H₂O)₆ ]²⁺  and   SO₄²⁻  ions.
 
  Cu SO₄ + 5 H₂O  ==>   ( Cu SO₄. 5 H₂O )  +  heat

  Cu SO₄ + 6 H₂O   ==>    Cu  (H₂O)₆²⁺   + SO₄²⁻  + heat
                            aqua