In Kjeldahl’s method for estimation of nitrogen present in the soil sample, ammonia evolved from 0.75g of sample neutralized 10ml of 1M H₂SO₄. The percentage of nitrogen in the soil is:

The Lassaigne’s extract is boiled with conc. ${\mathrm{HNO}}_3$ while testing for halogens, because it is:

1. Helps in the precipitation of $\mathrm{AgCl}$
2. Increases the solubility product of $\mathrm{AgCl}$
3. Increases the concentration of ${\mathrm{NO}}_3^{-}$ ions
4. Decomposes ${\mathrm{Na}}_2\mathrm{S}$ and $\mathrm{NaCN}$, if formed