When I mole of a monatomic gas is mixed with 3 moles of a diatomic gas, the value of adiabatic exponent γ for the mixture is:
53
1.5
1.4
139
n1+n2γ-1 = n1γ1-1+n2γ2-1
1+3γ-1 = 153-1+375-1
4γ-1 = 32+152 = 9
or γ-1 = 49 ⇒ γ = 1+49 = 139