Q.

The volume of an ideal gas increases 8 times and temperature becomes (14)th of the initial temperature during a reversible change. If there is no exchange of heat in this process (ΔQ=0), then identify the gas from the following options (assuming gases given in the options are ideal gases):          [2026]

1 CO2  
2 NH3  
3 O2  
4 He  

Ans.

(4)

PVγ=constant

TVγ-1=constant

TVγ-1=(T4)(8V)(γ-1)

4=8(γ-1)

22=23γ-3

2=3(γ-1)

γ=53

Gas is a monoatomic gas.

Answer is He.