Verified answer

Mr ((C2H4)n) = Ar (C) * N (C) + Ar (H) * N (H) = (12 * 2 + 1 * 4) * n = 28n;

ω (C) = N (C) * Ar (C) * 100% / Mr ((C2H4)n) = 2n * 12 * 100% / 28n = 85,71%.