Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in the figure.
(a) What will be the action of gas on
(i) dry litmus paper?
(ii) moist litmus paper?
Write a balanced chemical equation for the reaction taking place.
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Litmus is a natural indicator. A natural Indicator is a type of indicator that can be found naturally and can help us to know whether the material tested is an acidic substance or a basic substance. It is obtained from lichens. The process of obtaining a litmus solution needs the crushing and grinding of lichens.

Some examples of natural indicators other than litmus are:  red cabbage, turmeric, turnip skin, curry powder, etc.

It is used to test materials for acidity and basicity. This solution can also be used to differentiate between acids and bases. When acid is added to a litmus solution, it changes to red. When a base is added, it changes to blue. Neutral litmus paper is purple in colour.