Consider a mixture of n moles of helium gas and 2n moles of oxygen gas (molecules taken to be rigid) as an ideal gas. Its CP/CV  value will be :

For Heliummonoatomic gas cv1=32R and cp1=52R   Here n1=n​For oxygendiatomic gas cv2=52R and cp2=72R Here n2=2nγmix=n1cp1+n2cp2n1cv1+n2cv2=n52R+2n72Rn32R+2n52R=5+145+10=1913