Question bank/NEET UG/Physics

NEET UGPhysicsModerateRe-NEET 2026

The mean free path of molecules in an ideal gas A is half that of another ideal gas B. The diameter of the spherical molecules of gas A is twice the diameter of the molecules of B. If number densities of the gases A and B are nAn_A and nBn_B, respectively, the correct option is:

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Sol. λA=12λBλ_A = \frac{1}{2}λ_B
λ=12πd2nλ = \frac{1}{\sqrt{2} πd^2n}
dA=2dBd_A = 2d_B
λA=12πdA2nAλ_A = \frac{1}{\sqrt{2} πd_A^2n_A}
λB=12πdB2nBλ_B = \frac{1}{\sqrt{2} πd_B^2n_B}
λAλB=12=dB2nBdA2nA\frac{λ_A}{λ_B} = \frac{1}{2} = \frac{d_B^2 n_B}{d_A^2 n_A}
nAnB=2⋅dB2dA2\frac{n_A}{n_B} = \frac{2 \cdot d_B^2}{d_A^2}
nAnB=2⋅dB24dB2=12\frac{n_A}{n_B} = \frac{2 \cdot d_B^2}{4d_B^2} = \frac{1}{2}

Source: geekyrakshit/indian-exam-questions / reneet2026-code50

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