Question

which of these is an element? oxygen (o) salt (nacl) carbon dioxide (co2) water (h2o)

Explanation:

An element is a pure substance made of only one type of atom. Oxygen (O) is an element as it consists of oxygen - atoms only. Salt (NaCl) is a compound of sodium and chlorine, carbon - dioxide (CO2) is a compound of carbon and oxygen, and water (H2O) is a compound of hydrogen and oxygen.

Answer:

Oxygen (O)