The gas pressure in an oxygen tank is 3.90 atm at a
temperature of 298 K. If the pressure decreases to 3.20 atm,
what is the temperature of the gas in kelvin?

The answer to your question is   Temperature 2 = 244.5°K

Explanation:

Data

Pressure 1 = 3.90 atm

temperature 1 = 298°K

Pressure 2 = 3.20 atm

temperature 2 = ?

Process

1.- Use the Gay-Lussac law to solve this problem

         Pressure 1/Temperature 1 = Pressure 2/Temperature 2

-Solve for Temperature 2

         Temperature 2 = Temperature 1 x Pressure 2 / Pressure 1

-Substitution

         Temperature 2 = 298 x 3.20 / 3.90

-Simplification

         Temperature 2 = 953.6 / 3.90

-Result

          Temperature 2 = 244.5°K