KI solution is the reagent for :

All the options are correct. Potassium iodide solution is the reagent for lead, copper, silver and mercury ions.

The ions K+I make up the ionic compound known as potassium iodide. It forms crystals with the structure of sodium chloride. Industrial production of it involves iodizing KOH. With almost 37,000 tonnes produced in 1985, white salt is the most important iodide compound in terms of commerce.

Hence correct option is a, b, c, d