CO2−3 : On action of dil sulphuric acid, CO2 gas is released which turns lime water milky.
S2− : On action of dil sulphuric acid, H2S gas is released which turns lead acetate paper black.
SO2−3 : On action of dil H2SO4,SO2 gas is evolved which turns acidified potassium dichromate solution green.
NO−2: On action of dil H2SO4, brown coloured NO2 gas is evolved which turns Kl solution containing starch, blue.