ANS:B - CCl4

Among the options provided, the incombustible substance is sulfur (S). Sulfur is incombustible because it does not readily react with oxygen to produce heat and light, as combustion typically requires. The other options, H2 (hydrogen), CCl4 (carbon tetrachloride), and C2H2 (acetylene), are combustible substances that can react with oxygen to undergo combustion.