If an ideal gas is kept inside a container with movable piston, and is allowed to expand ISOTHERMALLY, then pressure exerted by the gas on the container wall decreses. Why?

What happens to the rate of collision of gas particles with container walls?

Isothermal expansion T = constant 

Hence PV = const

As for expansion volume increases hence pressure decreases 

As P = 1/2 rho V^2

as p decreases v decreases which is rms speed of gas molecules and thus rate of collision of gas particl;es in container decrease

pressure exerted by the gas walls on container is directly proportional to the rate of collisions. If pressure decreases then rate wil decrease to