The molar mass of an unknown gas was measured by an effusion experiment. It was found that the unknown gas effused at a rate of 2.5 × 10−6 mol/hr, whereas nitrogen gas effused at a rate of 3.3 × 10−6 mol/hr. The molar mass of the gas is

A) 32 g/mol.
B) 37 g/mol.
C) 24 g/mol.
D) 16 g/mol.
E) 48 g/mol.