Agas has a density of 0.902 g l at stp what is the molar mass of this gas

According to the molar gas volume, one mole of a gas occupies a volume of 22400 cm³ or 22.4 liters. The standard temperatures and pressures conditions are temperature of 0 degrees Celsius or 273 kelvin and an absolute pressure of 103.325 kPa or 1 atm. In this case, the density is 0.902 g/l and the volume is 22400 cm³,
therefore, the molar mass will be;
0.902 g/ L ×22.4 liters = 20.2048g 

Particle exchange energy though elastic collision , hope this .