First,let's assume ideal gas behavior for simplicity. This is a special case because the volumes of the two states are equal. At constant volume, we can use the Gay-Lussac equation:
P₁/T₁ = P₂/T₂
(0.8)/(127+273) = (P₂)/(27+273)
Solving for P₂,
P₂ = 0.6 atm
Thus, the answer is 0.6 atm.