A gas at 300 K occupies 6.50 dm3. What will its volume be at 250 K?

Answer 1

You would be doing yourself a much greater service if you spent this time reading your chemistry textbook so that you can answer this for yourself.

Answer 2

Using the ideal gas law,
PV = nRT
where P is the pressure, V is the volume, n is the number of moles, R is the gas rate constant, and T is the temperature,

one can solve for the unknown volume if the other 3 factors are either known or held constant.
Since the pressure and number of moles are held constant, we can simplify the equation to,
V1 / T1 = V2 / T2
this is known as Charles's Law.

6.50 dm^3 / 300 K = V2 / 250 K
Solving for V2,
V2 = 250 K * (6.50 dm^3 / 300 K)
V2 = 5.42 dm^3