What is the volume of 21.0 g of nitrogen gas at stp?

We can use the ideal gas law equation to find the volume of N₂ gas at STP

PV = nRT

where

P - standard pressure - 101 325 Pa

V - volume

n - number of moles - 21.0 g / 28 g/mol = 0.750 mol

R - universal gas constant - 8.314 Jmol⁻¹K⁻¹

T - standard temperature - 273 K

substituting the values in the equation

101 325 Pa x V = 0.750 mol x 8.314 Jmol⁻¹K⁻¹ x 273 K

V = 16.8 L

volume of N₂ at STP is 16.8 L