The correct option is C 1/2 atm
Given information:
Initial pressure of the gas P1=1 atm
Initial temperature of the gas T1=273∘C=546 K
Final temperature of the gas T2=0∘C=273 K
Final Pressure of the gas P2=?
From Gay Lussac's law, P1T1=P2T2 at constant volume.
1546=P2273
Hence,
P2=12 atm