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  9. Q90

UPPSC PCS 2025 · Question 90 of 150

Which of the following gases is/are lighter than air? Hydrogen chloride Sulfur dioxide Helium Select the correct answer from the code given below: Code:

Science

  1. AOnly 1
  2. BOnly 3Correct
  3. C1 and 2
  4. D2 and 3

Answer: B. Only 3

Explanation

To determine whether a gas is lighter or heavier than air, we compare its molecular weight with that of air (average ≈ 29 g/mol). Hydrogen chloride (HCl) – Molecular weight = 36.5 → heavier than air .

Source: selfstudywala.com UPPCS Prelims 2025 GS Paper 1 detailed solution (based on UPPCS official answer key)

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