The label of a fertilizer states that the fertilizer contains 18.1% p4o10 by mass. What is the mass percentage of phosphorus in the fertilizer?

The fertilizer contains 7.90 % P by mass.

Assume you have 100 g of fertilizer.

Mass of P₄O₁₀ = 100 g fertilizer * 18.1 g P₄O₁₀/100 g fertilizer = 18.1 g P₄O₁₀

M_r of P₄O₁₀ = 4 * 30.97 + 10 * 16.00 = 123.88 + 160.00 = 283.88

Mass of P = 18.1 g P₄O₁₀ * (123.88 g P/283.88 g P₄O₁₀) = 7.90 g P

Mass % P = mass/total mass * 100 % = 7.90 g / 100 g * 100 % = 7.90 %