The molar volume of an ideal gas at one atmosphere and ${273}^{\circ }\mathrm{C}$ is 

At 273 K and 1 atm pressure, gas occupies 22.4 litres molar volume. In the given question, pressure = 1 atm, n = 1 mol and temperature =273^oC=546K. Thus, at 546 K and 1 atm pressure, an ideal gas would occupy 44.8 litres of molar volume, as volume is directly proportional to temperature, at constant pressure. When the temperature doubles, the volume also doubles.