Apparatus : Coal, match box, moist litmus paper, etc.
Procedure : Ignite the coal. Hold the moist blue litmus paper over the gas released on igniting the coal. Note the observation
.

(a) With which gas in the air does the coal react on igniting?
(b) What is the substance formed?
(c) What change takes place in the litmus paper?
(d) Write down the chemical reaction taking place in the above procedure.