Tests for Alkaline Ammonia and Acidic/Reducing SO2

Steps:

• Identify ammonia (NH3) test: alkaline gas turns damp red litmus paper blue.
• Identify sulfur dioxide (SO2) test: acidic reducing gas decolorizes acidified potassium manganate(VII) from purple to colorless.
• Compare options: seek row pairing red litmus for NH3 and manganate(VII) for SO2.
• Select matching row as correct.

Why C is correct:

• Damp red litmus detects NH3's alkalinity (pH > 7, turns blue); acidified KMnO4 confirms SO2 via reduction (MnO4- + SO2 → Mn2+ + SO42-, decolorizes).

Why the others are wrong:

• A: Damp litmus (unspecified color) fails to specify red for NH3; no clear SO2 pairing.
• B: Both litmus types target pH but miss SO2's reducing test.
• D: Damp blue litmus redundant for NH3; no SO2 test included.

Final answer: C