Final answer:
The new pressure inside the container is 3 atm.
Step-by-step explanation:
To find the new pressure inside the container, we can use the combined gas law equation: PV/T = constant. Since the volume remains constant, we can simplify the equation to P1/T1 = P2/T2. Plugging in the initial values (P1 = 1.5 atm, T1 = 300 K) and the final values (T2 = 600 K), we can solve for P2: P2 = (P1 * T2) / T1 = (1.5 atm * 600 K) / 300 K = 3 atm.