Answer: D) CO
Explanation:
An element is the pure substance which contains same kind of particles.
A compound is formed when two or more elements combine together in a fixed ratio by mass.
Mg, Sn and H are elements whereas CO is a compound which is formed by combination of carbon and oxygen in the ratio of 12:16 by mass.
[tex]2C+O_2\rightarrow 2CO[/tex]
