Question

which of these is a compound?
carbon dioxide (co2)
nitrogen (n)
sand
aluminium (al)

Explanation:

A compound is a substance made up of two or more different chemical elements chemically bonded together. Carbon Dioxide is composed of one carbon atom and two oxygen atoms. Nitrogen is an element. Sand is a mixture mainly of silicon - dioxide and other substances. Aluminium is an element.

Answer:

Carbon Dioxide (CO2)