The correct option is A 75 K
Given,
Gas is ideal and monoatomic, so γ=53
Gas is undergoing adiabatic expansion, so the equation of state of the gas in terms of T and V is given by
T Vγ−1=k
From this, we can write that
TiVγ−1i=TfVγ−1f
or Tf=Ti(ViVf)γ−1
From the data given in the question,
Tf=300×(Vi8Vi)53−1=3004=75 K
Hence, option (a) is the correct answer.