Answer is: the molecular formula of a compound is P₇N₇Cl₁₄.
If we use 100 grams of substance:
ω(P) = 26.7% ÷ 100% = 0.267.
m(P) = 0.267 · 100 g = 26.7 g.
n(P) = 26.7 g ÷ 31 g/mol = 0.86 mol.
n(N) = 12.1 g ÷ 14 g/mol = 0.86 mol.
n(Cl) = 61.2 ÷ 35.45 g/mol = 1.72 mol.
n(P) : n(N) : n(Cl) = 0.86 mol : 0.86 mol : 1.72 mol/ 0.86 mol.
n(P) : n(N) : n(Cl) = 1 : 1 : 2.
M(PₓNₓCl₂ₓ) = 812 g/mol.
M(PₓNₓCl₂ₓ) = 31x + 14x + 70.9x · g/mol.
812 g/mol = 115.9x · g/mol.
x = 7.
