A solution turns red litmus blue. Its pH is most likely: (a) 1 (b) 4 (c) 5 (d) 10

Question

A solution turns red litmus blue. Its pH is most likely:
(a) 1
(b) 4
(c) 5
(d) 10

Accepted Answer

## Model Answer **(d) 10** A solution that turns red litmus blue is basic/alkaline. Basic solutions have pH greater than 7. Among the given options, only 10 is greater than 7, so the pH is most likely **10**. Source: Chapter 2, Section 2.3 (pH Scale) --- ## Explanation The key rule: **pH > 7 → basic** (turns red litmus blue); **pH < 7 → acidic**; **pH = 7 → neutral**. Options (a), (b), and (c) are all below 7 (acidic), so only (d) 10 is correct. Examiners award the mark for the correct option with a one-line justification.

Science — AI-generated practice question