Answer:
4 means there are four molecules of Na₂SO₃.
Step-by-step explanation:
Molecule:
A molecule is the smaller particle which can exist independently.
It may be monoatomic , diatomic, triatomic etc.
For example,
Hydrogen molecule consist of two atoms H₂
Nitrogen molecule = N₂
It may be combination of atoms of different elements.
HCl, H₂SO₄,Na₂SO₃
HCl = 1 mole of hydrochloric acid or one molecules of hydrochloric acid
H₂SO₄= 1 mole of sulfuric acid or one molecule of sulfuric acid
Na₂SO₃ = 1 mole of sodium sulfite or one molecule of sodium sulfite.
4Na₂SO₃ = 4 mole of sodium sulfite or four molecule of sodium sulfite.
The coefficient before the formula indicate the total number of molecules.