Two moles of helium are mixed with n moles of hydrogen. If Cp/Cv = 3/2 for the mixture, then the value of n is?

For a given mixture of gases, (n1+n2)/(γmix) =n1/(γ1)+n2/(γ2)
put n1=2, γmix=3/2, γ1=5/3, γ2=7/5
solving the required equation as
(2+n)/(3/2) = 2/(5/3) + n/(7/5)
n=2