O Levels Chemistry (5070)•5070/11/M/J/18
Explanation
Non-acidic gases neither donate H+ nor form acidic oxides in water.
Steps:
- Acidic gases react with water to form acids (e.g., H2CO3 from CO2, HNO3 from NO2).
- Basic gases like NH3 form bases (NH4OH); neutral gases like CH4 show no acid-base reaction.
- Evaluate pairs: both must lack acidic properties.
- Select pair where neither gas produces H+ in solution.
Why A is correct:
- Ammonia (NH3) is basic, forming NH4OH; methane (CH4) is neutral, inert in water.
Why the others are wrong:
- B: Carbon dioxide (CO2) forms acidic H2CO3.
- C: Nitrogen dioxide (NO2) forms acidic HNO3/HNO2.
- D: Both CO2 and NO2 form acids in water.
Final answer: A
Topic: The characteristic properties of acids and bases
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