Which of the following compounds is formed when magnesium burns in air?

Solution

1. Magnesium is highly reactive and burns in air to form magnesium oxide.
2. Simultaneously, magnesium also reacts with atmospheric nitrogen to form magnesium nitride.
3. The reactions are $2\text{Mg}+{\text{O}}_2\to 2\text{MgO}$ and $3\text{Mg}+{\text{N}}_2\to {\text{Mg}}_3{\text{N}}_2$.
4. Hence the answer is (C).