Which substance is a molecule?

1. Ch4

2. NaF

3. Ar

4. Pb

In fact, all of these (Ch4, NaF, Ar, and Pb) are molecules.

Molecules are substances that contain two or more elements, if these elements are different, then the substance is also a compound.

However, considering only the definition of a molecule, it is evident that both CH4 and NaF are molecules as they contain more than one element.