Given here, mOmAr=23.
As argon is monoatomic gas, so it has three degree of freedom (f) and oxygen is a diatomic gas, so its degree of freedom is five.
We know that average kinetic energy per molecule is given by KE=2fkT, where, k is Boltzmann's constant and T is temperature.
Here, T=27∘C is fixed for both gas.
So, (KE)O(KE)Ar=25kT23kT=53