Answer is 334.35 g.
Step-by-step explanation:
n = m/M
Where n is the number of moles of given substance (mol), m is the mass (g) and M is the molar mass of the substance (g/mol).
n = 3.99 mol
m = ?
M = 83.798 g/mol
By applying the formula,
3.99 mol = m / 83.798 g/mol
m = 3.99 mol x 83.798 g/mol
m = 334.35 g