O Levels Chemistry (5070)•5070/12/O/N/22
Explanation
pH Scale and Acid Neutralization Steps:
- Classify substances by pH: acidic (<7), neutral (=7), alkaline (>7).
- P (3.6) is acidic; Q (10.4) and R (7.8) are alkaline.
- Stomach acid is strongly acidic (pH 1–3); excess requires an alkaline substance for neutralization.
- R (pH 7.8, mildly alkaline) suits safe consumption and acid neutralization.
Why C is correct:
- Bases with pH >7 neutralize acids via the reaction: acid + base → salt + water, reducing excess stomach acidity.
Why the others are wrong:
- A: pH 3.6 <7 makes P acidic, not alkaline.
- B: Not enough information; table lists "some substances," so Q may not have the highest pH.
- D: Not enough information; S is not listed in the provided table.
Final answer: C
Topic: The characteristic properties of acids and bases
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