Name the type of reaction for the following:
$(i)$ Silver items turning black when left exposed to air.
$(ii)$ Change in colour of copper sulphate from blue to green on dipping an iron nail in it.

(N/A) $(i)$ Corrosion (Oxidation reaction): Silver reacts with sulfur compounds in the air to form silver sulfide $(Ag_2S)$,which is black in color.
$(ii)$ Displacement reaction: Iron $(Fe)$ is more reactive than copper $(Cu)$,so it displaces copper from the copper sulphate $(CuSO_4)$ solution to form ferrous sulphate $(FeSO_4)$,which is green in color.