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) $2.7 \times 10^{25}$
$p = nk_BT$, so $n = \dfrac{p}{k_BT} = \dfrac{1.01 \times 10^5}{1.38 \times 10^{-23} \times 273} \approx 2.7 \times 10^{25}$ m$^{-3}$.
Solution by Sreeraj P, M.Sc Physics