Give the characteristic tests for the following gases :

(a) CO2 gas : It is a colourless and odourless gas. When passed through lime water, it will initially become milky.

(b) SO2 gas : It is a colourless but a pungent smelling gas. The gas when passed through an acidified solution of potassium permanganate (pink) will decolourise it.

Similarly the gas when passed through an acidified solution of potassium dichromate (orange) will make it light green.

(c) Oxygen gas : The gas is a supporter of combustion. It can be tested by bringing a burning or smouldering match-stick near the mouth of the

test tube from which the gas escapes. The match-stick will burn more brightly.

(d) Hydrogen gas : The gas itself is combustible. It will burn with a pop sound when a burning candle or match- stick is brought near it.

2H2 (g) + O2 (g) ———-> 2H2O (g)