Answer: P = 7.1 atm
Explanation: For this problem we will use Combined Gas Law to solve for the new pressure. But never forget to convert the unit of temperature to Kelvin.
P1V1 /T1 = P2V2/ T2, Derive for P2.
P2 = P1V1T2 / T1V2
= 1.00 atm ( 3.00 L ) ( 323 K) / 273 K ( 0.50 L )
= 7.1 atm
Cancel out the units of L and K and the unit remains is in atm.