The pressure inside a hydrogen-filled container was 2.10 atm at 21 ∘ c. what would the pressure be if the container was heated to 85 ∘ c ? express your answer with the appropriate units.

Gay-Lussac's law described the relation between the pressure and the temperature of a gas at a certain volume.
His law states that: "At constant volume, the pressure of the gas is directly proportional to the temperature."
P/T = constant

This can be written as:
P1 /T1 = P2 / T2 where:
P1 is the initial pressure = 2.1 atm
T1 is the initial temperature = 21 + 273 = 294 degrees kelvin
P2 is the final pressure that we need to calculate
T2 is the final temperature = 85 + 273 = 358 degrees kelvin

Substitute with the givens in the above relation to get the value of P2 as follows:
(2.1) / (294) = P2 / (358)
P2 = 358 * (2.1/294)
P2 = 2.557 atm