Формула соединения серы, в котором массовая толика серы 50%: 1)SO3 2)H2SO3

Mr (SO₃) = Ar (S) * N (S) + Ar (O) * N (O) = 32 * 1 + 16 * 3 = 82;
(S в SO₃) = N (S) * Ar (S) * 100% / Mr (SO₃) = 1 * 32 * 100% / 80 = 40%;
Mr (H₂SO₃) = Ar (H) * N (H) + Ar (S) * N (S) + Ar (O) * N (O) = 1 * 2 + 32 * 1 + 16 * 3 = 82;
(S в H₂SO₃) = N (S) * Ar (S) * 100% / Mr (H₂SO₃) = 1 * 32 * 100% / 82 = 39,02%;
Mr (SO₂) = Ar (S) * N (S) + Ar (O) * N (O) = 32 * 1 + 16 * 2 = 64;
(S в SO₂) = N (S) * Ar (S) * 100% / Mr (SO₂) = 1 * 32 * 100% / 64 = 50%;
Mr (H₂SO₄) = Ar (H) * N (H) + Ar (S) * N (S) + Ar (O) * N (O) = 1 * 2 + 32 * 1 + 16 * 4 = 98;
(S в H₂SO₄) = N (S) * Ar (S) * 100% / Mr (H₂SO₄) = 1 * 32 * 100% / 98 = 32,65%.

Ответ: вариант 3).