How many moles of nitrous oxide gas (N2O) is contained in 20.0 L balloon at a pressure of 1.09 atm and a temperature of 298K?

There are 0,89 moles of nitrous oxide gas  in the balloon.

Explanation:

We apply the formula of the ideal gases, we clear n (number of moles); we use the ideal gas constant R = 0.082 l atm / K mol:

PV= nRT ---> n= PV/RT

n= 1,09 atm x 20,0 L /0.082 l atm / K mol x 298 K

n= 0,89212637 mol