The mass number of tin (Sn) is typically 118.71. However, tin has several isotopes, and its most stable isotopes are tin-112, tin-114, tin-115, tin-116, tin-117, tin-118, tin-119, and tin-120. Among these, the most common isotope of tin is tin-120, which has a mass number of 120.
The mass number is the total number of protons and neutrons in the nucleus of an atom. For tin, the atomic number is 50, indicating it has 50 protons. The varying number of neutrons in its isotopes affects the overall mass number, leading to the different isotopes of tin.