Which of the following solutions will not change the colour of blue litmus paper to red? 1. Acid solution 2. Base solution 3. Common salt solution Select the correct answer using the code given below.

Litmus paper is a natural pH indicator derived from lichens used to distinguish between acidic and basic substances [1]. Acids have a pH less than 7 and specifically change the color of blue litmus paper to red [1]. In contrast, bases (alkalis) have a pH greater than 7 and do not turn blue litmus red; instead, they turn red litmus paper blue [1]. Common salt (sodium chloride) is a neutral salt formed from a neutralization reaction, resulting in a solution with a pH close to 7 [1]. Neutral solutions do not exhibit acidic or basic properties and therefore do not change the color of either red or blue litmus paper. Consequently, both base solutions and common salt solutions will not change blue litmus to red, making option 2 (2 and 3) the correct choice.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > p. 17