How many moles of O2 are in a flask with a volume of 0.45 L at a pressure of 320 kPa and a
temperature of 280K?
What Law is used to solve?

I just need to know the Law and and explanation please I dont understand how it could be any law since it has pressure, volume, and temperature.

0.0833 moles of O₂

Explanation:

Most usual Law to solve this sort of problem, is the Ideal Gases Law

Pressure .  Volume = number of moles .  R . Temperature

where R is the Ideal Gases Constant → 0.082 L.atm/mol.K

First of all we need to convert the pressure from kPa to atm, because the Units of R

320 kPa . 1  atm / 101.3 kPa = 3.16 atm

Now, you replace data:

3.16 atm . 0.45L = mol . 0.082 L.atm/mol.K . 280K

(3.16 atm . 0.45L) / (0.082 L.atm/mol.K . 280K) = mol

0.0833 moles of O₂