Q37 / 150 · MHT CET 2025 (21 Apr Shift 2) · Chemistry

The mass of $4.48 \mathrm{dm}^3$ of certain gas is 5.6 g at STP. Assuming ideal behaviour, identify the probable gas from following.

  • A
    $\mathrm{Cl}_2$
  • B
    $\mathrm{O}_2$
  • Correct answer
    C
    $\mathrm{N}_2$
  • D
    $\mathrm{CH}_4$

Solution

The molar mass is determined from the gas sample's mass and volume at STP, where 1 mole occupies $22.4\ \mathrm{dm}^3$.

The number of moles is $n = \frac{4.48\ \mathrm{dm}^3}{22.4\ \mathrm{dm}^3\cdot\mathrm{mol}^{-1}} = 0.2\ \mathrm{mol}$.

Molar mass is calculated as $M = \frac{5.6\ \mathrm{g}}{0.2\ \mathrm{mol}} = 28\ \mathrm{g}\cdot\mathrm{mol}^{-1}$.

Comparing with the options: C $\mathrm{N}_2$ ($2 \times 14 = 28\ \mathrm{g}\cdot\mathrm{mol}^{-1}$) matches the calculated molar mass.

Hence, the correct answer is option: 'C'.

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