The mean free path of molecules of an ideal gas is given as: λ=
V
√2πd2N
where : V= Volume of container N= No of molecules Hence with increasing temp since volume of container does not change (closed container), so mean free path is unchanged. Average collision time=
mean free path
Vav
=
λ
(avg speed of molecules)
∵ avg speed α√T ∴ Avg coll. time α
1
√T
Hence with increase in temperature the average collision time decreases.