Here's how to calculate the mass of 0.7891 mol of ferric oxide (Fe₂O₃):

1. Find the molar mass of Fe₂O₃

* Iron (Fe) has a molar mass of 55.845 g/mol.

* Oxygen (O) has a molar mass of 15.9994 g/mol.

Molar mass of Fe₂O₃ = (2 * 55.845 g/mol) + (3 * 15.9994 g/mol) = 159.69 g/mol

2. Use the formula: mass = moles * molar mass

mass = 0.7891 mol * 159.69 g/mol = 126.0 g

Therefore, the mass of 0.7891 mol of ferric oxide (Fe₂O₃) is 126.0 g.