Question

Assertion: When a piece of moist red litmus paper is placed in a gas jar of ammonia it turns blue.
Reason: The ammonia gas is basic in nature and this property converts the red litmus to blue.
A.Both assertion and reason are correct and reason is the correct explanation of the assertion.
B.Both assertion and reason are correct but reason is not the correct explanation of the assertion.
C.Assertion is correct, but reason is incorrect.
D.Both Assertion and reason are incorrect.

Answer 1

Hint: The litmus paper is used to test the nature of the solution under consideration based on the change in the colour, the substances can be acidic, basic and neutral in nature as per the number of Hydronium ($H^+$) and Hydroxyl ions ($O{H^-}$) present in the solution.

Complete step by step answer:
The litmus paper is used to test the nature of the solution under consideration based on the change in the colour, the substances can be acidic, basic and neutral in nature as per the number of Hydronium (H+) and Hydroxyl ions (OH-) present in the solution.
Litmus paper is obtained from lichens which are used for the dyeing purpose. Litmus paper is of two types the blue and red litmus paper. Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic or alkaline conditions. The change in the colour is due to the pH of the solution reflected through the colour change in the molecule.

When the litmus blue litmus paper is dipped in ammonia solution which is basic in nature it turns to red colour due to the change in the pH of the solution and thus the colour change is observed in the solution since the number of Hydroxyl ions is more than the number of the hydronium ions. Thus both assertion and reason are correct and reason is the correct explanation of the assertion

So, the correct answer is Option A .

Note:
 pH scale is used to determine the number of the Hydronium ions in the solution. The range of the scale is from 0-14 with 0-6 being acidic, 7 is neutral and 8-14 being basic with the increase in the range of the scale the basicity of the solution increases.