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