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NEET CHEMISTRYEasy

Which of the following contains the highest number of helium atoms?

A

4 u of helium

B

4 g of helium

C

2.27 L of helium at STP

D

4 mol of helium

Step-by-Step Solution

  1. Analyze Option A (4 u): The unified atomic mass unit ('u') represents the mass of a single atom on the atomic scale. Since the atomic mass of Helium is 4 u, this option corresponds to exactly 1 atom.
  2. Analyze Option B (4 g): The molar mass of Helium is 4 g mol−14 \text{ g mol}^{-1}. Moles=4 g4 g mol−1=1 mol\text{Moles} = \frac{4 \text{ g}}{4 \text{ g mol}^{-1}} = 1 \text{ mol} Total atoms = 1×NA=6.022×10231 \times N_A = 6.022 \times 10^{23} atoms [Class 11 Physics, Appendix A 3].
  3. Analyze Option C (2.27 L at STP): Using the standard molar volume at STP (22.7 L mol−122.7 \text{ L mol}^{-1} for 1 bar pressure): Moles=2.27 L22.7 L mol−1=0.1 mol\text{Moles} = \frac{2.27 \text{ L}}{22.7 \text{ L mol}^{-1}} = 0.1 \text{ mol} Total atoms = 0.1×NA0.1 \times N_A atoms.
  4. Analyze Option D (4 mol): Total atoms = 4×NA4 \times N_A atoms.
  5. Conclusion: Comparing the magnitudes: 4NA4 N_A (Option D) > 1NA1 N_A (Option B) > 0.1NA0.1 N_A (Option C) > 1 atom (Option A).
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