Why is it necessary to use acetic acid and not sulphuric acid for acidification of sodium extract for testing sulphur by lead acetate test?

Explanation

For testing of sulphur present in the organic compound lassaigne's extract is acidified with acetic acid `(CH_3COOH)` and not sulphuric acid bacause lead acetate is soluble and does not interfere with the test. If sulphuric acid `(H_2SO_4)` is used, lead acetate will react with `H_2SO_4` itself to form white precipitate of `PbSO_4` as follows
`Pb(CH_3COO)_2+H_2HO_4rarrPbSO_4darr+2CH_3COOH`
The white precipitate of `PbSO_4` so formed will interfere with this test of sulphur.
`Pb(CH_3COO)_2+Na_2SrarrPbSdarr+2CH_3COONa`