A flask contains a monoatomic and a diatomic gas in the ratio of 4 ∶ 1 by mass at a temperature of 300K The ratio of average kinetic energy per molecule of the two gases is 

Concept:

The average kinetic energy per molecule of a gas is given by the formula:

K.E. = (3/2) k T

where k is the Boltzmann constant and T is the temperature in Kelvin.

Calculation:

Given that the temperature (T) is 300K for both gases, the average kinetic energy per molecule for monoatomic and diatomic gases can be calculated as follows:

⇒ For monoatomic gas, K.E._monoatomic = (3/2) k T

⇒ For diatomic gas, K.E._diatomic = (3/2) k T

Since the temperature is the same for both gases:

⇒ K.E._monoatomic = K.E._diatomic

Conclusion:

∴ The ratio of average kinetic energy per molecule of the two gases is 1 ∶ 1.

Hence, the correct answer is option 1.