Here's how to calculate the mass of 0.0250 mol of P₂O₅:

1. Find the molar mass of P₂O₅

* Phosphorus (P) has a molar mass of 30.97 g/mol.

* Oxygen (O) has a molar mass of 16.00 g/mol.

Molar mass of P₂O₅ = (2 * 30.97 g/mol) + (5 * 16.00 g/mol) = 141.94 g/mol

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

mass = 0.0250 mol * 141.94 g/mol = 3.55 g

Therefore, the mass of 0.0250 mol of P₂O₅ is 3.55 grams.