Hello sir

We know that molar specific heat or molar heat capacity is the amount of energy i.e. ( heat energy) re quired  to increase the temperature of a substance of one mole And monatomic gases are the gases which are free to move here and there.

So, ratio of molar specific heat is Cp/Cv. We know that value of Cp and Cv for monatomic gases is 5R/2 and 3R/2. Then according to formula (Cp/Cv) is (5R/2)/(3R/2) = 1.66