What representative units define molecular compounds and ionic compounds?

The molecular formula of the compounds indicates the amount of atoms that the substance contains. For example, water whose formula is H2O contains 2 atoms of hydrogen and 1 of oxygen. The representative unit of a molecular compound is a molecule while ions are represented by a formula unit.

Mole can be a unit 6.02 × 10²³. The units may be electrons, atoms, ions, or molecules, depending on the nature of the substance

Explanation:

it's c. elements are placed in rows based on how may valencies electrons have.