The correct answer is option 2, which states that bronze is an alloy of copper (Cu) and tin (Sn).

An alloy is a mixture of two or more metals, and bronze is one of the oldest known alloys. It is typically composed of around 90% copper and 10% tin, although the exact composition may vary.

Option 1, which suggests that bronze is an alloy of copper and zinc (Zn), is incorrect. While copper and zinc do form an alloy called brass, bronze is distinctly different and does not contain zinc.

Option 3, which states that bronze is an alloy of zinc and magnesium (Mg), is also incorrect. Bronze does not contain magnesium.

Option 4, which suggests that bronze is an alloy of iron (Fe) and copper, is also incorrect. Bronze does not contain iron.

In conclusion, the correct composition of bronze is copper and tin, making option 2 the accurate answer.