How dou you show the presence of both iodide and sulfate in a mixture?

You can show the presence of Sulphate in a mixture by adding barium chloride solution followed by dil HCl. A white precipitate that does not dissolvev in dil HCl indicates the presence of sulphate ioins.

Ba2+ (aq) + SO4^2- (aq) ---------> BaSO4 (s)

Iodide ions can be shown by adding to the suspected iodide a solution of lead nitrate where upon a brilliant yellow ppt is thrown down

Pb2+ (aq) + 2 I- (aq) --------> PbI2 (aq)

Also addition of silver nitrate will give a yellow ppt which is insoluble in ammonia solution.

Ag+ (aq) + I- (aq) ----------> AgI (s)