The mean free path of molecules of a gas, (radius r) is inversely proportional to

A monatomic gas at a pressure P, having a volume V expands isothermally to a volume 2V and then adiabatically to a volume 16V. The final pressure of the gas is (Take $$\gamma $$ = 5/3)

The oscillation of a body on a smooth horizontal surface is represented by the equation,
X = A cos$$\left( {\omega t} \right)$$
where X = displacement at time t
$$\omega $$ = frequency of oscillation
Which one of the following graphs shows correctly the variation a with t?
Here a = acceleration at time t
T = time period

The number of possible natural oscillations of air column in a pipe closed at one end length 85 cm whose frequencies lie below 1250 Hz are (Velocity of sound = 340 m s^$$-$$1)