Q 11-12-025NEETJEE MainMedium
The number of molecules per cubic metre of an ideal gas at $1.01 \times 10^5$ Pa and $273$ K is about ($k_B = 1.38 \times 10^{-23}$ J K$^{-1}$)
Answer: (C) $2.7 \times 10^{25}$
Concept. $p = nk_BT$.
Step 1. Solve.
$$n = \frac{1.01 \times 10^5}{1.38 \times 10^{-23} \times 273} \approx 2.7 \times 10^{25}\ \text{m}^{-3}$$
Answer. $2.7 \times 10^{25}$ (Option C).
Solution by Sreeraj P, M.Sc Physics