Which of the following contain the same number of atoms?
(Given : Molar mass in g mol$$^{-1}$$ of H, He, O and S are 1, 4, 16 and 32 respectively)
A. 2 g of O$$_2$$ gas
B. 4 g of SO$$_2$$ gas
C. 1400 mL of O$$_2$$ at STP
D. 0.05 L of He at STP
E. 0.0625 mol of H$$_2$$ gas
Choose the correct answer from the options given below :

The total number of atoms present is calculated using

$$\text{Number of atoms}=\text{Number of moles}\times\text{Atomicity}\times N_A.$$

For (2\text{ g}) of (O_2),

$$n=\frac{2}{32}=0.0625\text{ mol},$$

so the total number of atoms is

$$0.0625\times2=0.125N_A.$$

For (4\text{ g}) of (SO_2),

$$n=\frac{4}{64}=0.0625\text{ mol},$$

so the total number of atoms is

$$0.0625\times3=0.1875N_A.$$

For (1400\text{ mL}) of (O_2) at STP,

$$n=\frac{1.4}{22.4}=0.0625\text{ mol},$$

so the total number of atoms is

$$0.0625\times2=0.125N_A.$$

For (0.05\text{ L}) of He at STP,

$$n=\frac{0.05}{22.4}\approx0.0022\text{ mol},$$

so the total number of atoms is

$$0.0022N_A.$$

For (0.0625\text{ mol}) of (H_2),

$$\text{Total atoms}=0.0625\times2=0.125N_A.$$

Hence,

• A: (0.125N_A) atoms
• B: (0.1875N_A) atoms
• C: (0.125N_A) atoms
• D: (0.0022N_A) atoms
• E: (0.125N_A) atoms

Therefore, the substances containing the same number of atoms are A, C and E.