The correct option is D a chemical change occurs.
Iron nail, when dipped in a blue-coloured copper sulphate solution, reacts with it. The reaction causes a change in the colour of the solution from blue to green due to the formation of iron sulphate. A brownish deposit of copper is deposited on the iron nail. The reaction is repesented as:
Copper sulphate + Iron → Iron sulphate + Copper
The given reaction involves a chemical change since there is a formation of a new substance along with change in colour.