Concept:Gun metal is a type of bronze, specifically an alloy of copper with tin and zinc.Explanation:Gun metal, also known as red brass, is mainly composed of copper (Cu), tin (Sn), and zinc (Zn). Its typical composition is 88% copper, 8–10% tin, and 2–4% zinc. This alloy was historically used for making guns and bullet casings. Today, it is used for heavy machinery parts because it can withstand high pressure and resists corrosion. Among the given options, only option B (Cu + Sn + Zn) matches the correct composition of gun metal. Option A (Sn + Pb + Sb) is type metal, option C (Sn + Pb) is solder, and option D (Cu + Zn + Ni) is nickel silver.Answer:B. Cu + Sn + Zn