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NDA 1 2025 GAT, question 79

Topic: Chemistry

Q79

Which one of the following statements is NOT correct?

  1. (a) Half mole of nitrogen gas is measured 11.2 litre at STP
  2. (b) 17 gram of ammonia gas contains 6.022×10236.022 \times 10^{23} molecules at STP
  3. (c) 22.4 litre of CO2CO_{2} gas at STP contains 44 gram of molecules
  4. (d) 4 gram of hydrogen gas contains 6.022×10236.022 \times 10^{23} moleculesCorrect answer

Solution.

Answer: (d) 4 gram of hydrogen gas contains 6.022×10236.022 \times 10^{23} molecules

  1. Hydrogen gas is H2H_{2}, with molar mass approximately 2 g mol⁻¹.
  2. Hence 4 g is 2 moles and contains 2NA=1.2044×10242N_{A} = 1.2044 \times 10^{24} molecules, not one Avogadro number.
  3. The other statements use the standard school convention of 22.4 L mol⁻¹ at STP.