The correct option (B) 0°C
Explanation:
Vrms of He = (5/6) Vrms of H2
TH2 = 0°C = 273K
THe = ρ
As Vrms = √(3RT / Mo) i.e. Vrms = √(T / MO)
∴ (Vrms He/Vrms H2) = √{(THe/MOHe) × (MOH2/TH2)}
∴ (5/7) = √({THe/273} × {2/4}) ----- molecular mass of He = 4 & of H2 is 2
∴ (5/7) = √(THe/546)
∴ (25/49) = (THe/546)
∴ THe = 278K
≈ 273 K
≈ 0°C