JEE Main · 2025 · 07 Apr 2025 · Shift 2 · Heat & Thermodynamics

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The helium and argon are put in the flask at the same room temperature ( 300 K ). The ratio of average kinetic energies (per molecule) of helium and argon is :
(Give : Molar mass of helium

= 4 g / mol

, Molar mass of argon

= 40 g / mol

)

(A) $1 : 10$
(B) $10 : 1$
(C) $1 : 10$
(D) $1 : 1$ ✓ Correct

Answer: (D)

Solution

The average kinetic energy per molecule depends only on temperature,

⟨ K E ⟩ = \frac{3}{2} k T

for a monoatomic gas, and is independent of molecular mass. Helium and argon are both monoatomic and are held at the same

300 K

, so their average kinetic energies per molecule are equal, in the ratio

1 : 1

JEE Main · 2025 · 07 Apr 2025 · Shift 2 · Single correct option

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