Question

Give only one suitable chemical test to identify the folliwing gases 1. Sulphur dioxide 2. Carbon dioxide 3. Oxygen 4. Hydrogen

Answer 1

Oxygen -Ignites a glowing splint since oxygen supports combustion
(O2)
Hydrogen -"Pop Test" : a lit taper will produce an audible "pop" when placed in   (H2)            hydrogen gas
Carbon dioxide - When CO2(g) is bubbled through colourless limewater 
(CO2)                  (Ca(OH)2(aq)) the limewater turns milky due to the
                           formation of a calcium carbonate (CaCO3(s)) precipitate.

                            When CO2(g) is bubbled through Ba(OH)2(aq) a 

white precipitate of BaCO3(s) forms.

Sulfur dioxide 
(SO2)             - SO2(g) is bubbled through hydrogen peroxide solution (H2O2) to produce sulfuric acid (H2SO4). The addition of barium chloride solution (BaCl2(aq)) to this solution results in a precipitate of barium sulfate (BaSO4(s)).

SO2(g) passed through a concentrated, acidified solution of potassium dichromate (K2Cr2O7) causes the dichromate solution to change colour from orange to green due to the formation of chromium(III) ions (Cr3+).