When Ideal gas has no volume, you use PV = nRT formula to find that Temperature equals to zero Kelvin. Next you use the formula K = 273 + Celsius and you will find that Celsius is -273 deg C when Kelvin equals to zero.
for PV = nRT , you will want to use 0.0831 because the unit is L-atm / mole-K. Both volume and pressure are used in the equation. The R constant 8.314 is J/mole-K and there is no volume or pressure in there, so you cannot use this. When you are solving any chemistry problem, the first thing you will look at is the unit. This will give you clue how to solve the problem. Sometimes the unit even helps you eliminate the answer choices that are wrong.