The number of atoms in $52 \mathrm{~g}$ of $\mathrm{He}$ is

The number of atoms in $52 \mathrm{~g}$ of $\mathrm{He}$ is
  1. $78.299 \times 10^{24}$ atoms
  2. $7.820 \times 10^{-24}$ atoms
  3. $7.829 \times 10^{24}$ atoms
  4. $78.234 \times 10^{25}$ atoms

Solution

Number of atoms $=\frac{N_A \times \text { mass }}{\text { At. mass }}$ $=\frac{6.023 \times 10^{23} \times 52}{4}=7.829 \times 10^{24}$ atoms

Asked in: MHT CET Full Test 1

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