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Question:

The molar specific heat of a gas as given from the kinetic theory is 5/2R. If it is not specified whether it is Cp or Cv, one could conclude that the molecules of the gas are:

Are definitely monoatomic

Are definitely rigid diatomic

Are definitely non-rigid diatomic

Can be monoatomic or rigid diatomic

Solution:

The correct option is D Can be monoatomic or rigid diatomic
The value of Cp is given as (f/2 + 1)R and that of Cv is given as (f/2)R
Hence the possible values of f for Cp or Cv to be 5/2R are 3, 5 respectively.
The degrees of freedom for a monoatomic gas is 3.
The degrees of freedom for a rigid diatomic gas is 5.
Hence correct answer is option D.