Question

P is an aqueous solution of acid and Q is an aqueous solution of base. When these two are diluted separately, then:

• A. The pH of P and Q increases
• B. The pH of P and Q decreases
• C. The pH of P increases, and the pH of Q decreases
• D. The pH of P decreases, and the pH of Q decreases till pH in each case is 7

Answer 1

The correct option is C

The pH of P increases, and the pH of Q decreases

Explanation of correct option.

Option (C ) is correct.

• Dilution means adding water to an aqueous solution.
• On diluting an acidic solution, the solution becomes less acidic, and its pH increases and approaches 7.
• On diluting a basic solution, the solution becomes less basic, and its pH decreases and approaches 7. Later the solution becomes neutral.

Explanation of incorrect options:

Option (A) The pH of P and Q increases.

• The pH of P will increase because it is an acid and it will become less acidic resulting in increased pH.
• The pH of Q will not increase because when a base is diluted it becomes less basic which decreases the pH.
• Hence, option(A) is incorrect .

Option (B) The pH of P and Q decreases.

• The pH of Q will decrease because it is a base and it will become less basic resulting in decreased pH.
• The pH of P will not decrease because when acid is diluted it becomes less acidic which increases the pH.
• Hence, option(B) is incorrect .

Option (D) The pH of P decreases, and the pH of Q decreases till the pH in each case is 7.

• The pH of Q will decrease because it is a base and it will become less basic resulting in decreased pH and approaching 7.
• The pH of P will not decrease because when acid is diluted it becomes less acidic which increases the pH and approaches 7.
• Hence, option(D) is incorrect.

Therefore, option (C) is the correct answer.