Give reason:

Why does sulphur dissolve when carbon disulphide is added to a mixture of iron and sulphur but not when it is added to iron sulphide ?

Iron is grey coloured and sulphur is a yellow substance. When we form a mixture of iron and sulphur, they retain their individual property, but when you heat this mixture, it will form a compound called as iron sulphide.
So, when we dissolve the mixture of iron and sulphur in Carbon disulphide, sulphur dissolves to form yellow coloured solution leaving behind iron at the bottom. In case of iron sulphide compound, it will not dissolve and settles down at the bottom.