Question

A colourless gas is dissolved in water and the resulting solution turns red litmus blue. Which of the following gases shows this type of reaction?

• A. $HCl$
• B. $H_{2}S$
• C. ${SO}_2$
• D. ${NH}_3$

Answer 1

Answer: (D)

${NH}_3$

${NH}_3$ is a colourless gas and a Lewis base. It's aqueous solution is alkaline in nature. Hence, when ${NH}_3$ is dissolved in water, the resulting solution turns red litmus blue. On the other hand, $HCl$, $H_{2}S$ and ${SO}_2$ gases are lewis acids. Their aqueous solutions are acidic in nature. When these gases are dissolved in water, the resulting solution turns blue litmus red.