Question

when crystals of copper sulphate are strongly heated the residue obtained is

Answer 1

Blue in color
Hope this helped you

Answer 2

Hio....

The copper Sulphate crystals are blue in colour due to the water of crystallization.

Hydrous copper Sulphate CuSO4•5H20 when heated loses its water of crystallization and becomes CuSo4

That is,
CuSO4•5H2O + Heat → CuSo4

It also loses it's colour on heating and becomes white.

Hope it is clear enough to understand and helpful… ^_^
#BeCurious