(a) Add a few drops of water in the test tube containing gas. Now, cover the test tube and shake it well. After shaking, test the solution with blue litmus and red litmus. It will turn blue litmus red. Thus, the gas is acidic in nature.
(b) Charcoal reacts with oxygen to form carbon dioxide gas.
C + O2 → CO2 ↑
Carbon from charcoal Oxygen Carbon dioxide
Carbon dioxide reacts with water to form carbonic acid, which turns blue litmus paper red.
CO2 + H2O → H2CO3
Carbon dioxide Water
Carbonic Acid (Turns blue litmus red)