Step-by-step explanation:
The number present as a subscript in a chemical formula depicts the number of atoms of each element present in the compound.
For example, in
here no subscript is present below Na, H and C atoms.
This means that only one atom of Na, one atom of C and one atom of H are present in a molecule of
.
Since, subscript 3 is present below O atom. This means that 3 atoms of oxygen are present in a molecule of
.