Question

why it is necessary to add few drops of conc. H2SO4 in the preparation of F.A.S. solution​

Answer 1

The reason why you add sulfuric acid before adding water is that the oxidation of the ferrous ion by dissolved oxygen in water is fast at neutral to high pH. By dissolving FAS in water with no acid added and watching the solution turn a cloudy orange, indicating the formation of ferric Ions.

Answer 2

Answer:

To prevent hydrolysis and to get clear solution