Calculate the mass of phosphorus that must be burned in oxygen to obtain phosphorus (5) oxide weighing 3.55 g?

Phosphorus can be burned with oxygen to oxide, not acid. Reaction equation: 4P + 5O2 = 2P2O5
According to the periodic table, we find the molar mass of phosphorus M = 31 g / mol. And phosphorus oxide M = 31 * 2 + 16 * 5 = 142 g / mol.
Find the amount of oxide: n = m / M = 3.55 g / 142 g / mol = 0.025 mol.
According to the reaction from 4 mol of phosphorus, 2 mol of oxide is obtained, which means n (P) / 4 = 0.025 / 2. Hence n (P) = 4 * 0.025 / 2 = 0.05 mol.
Find the mass of phosphorus: m = n * M = 0.05 mol * 31 g / mol = 1.55 g.
Answer: the mass of phosphorus is 1.55 g.