b) Club soda is a manufactured form of carbonated water, commonly used as a drink mixer. Sodium bicarbonate, potassium sulfate, potassium bicarbonate, potassium citrate, or sodium citrate is artificially added to replicate constituents commonly found in natural mineral waters
It represents the <em>number of atoms</em> of that particular element present in the compound. In C₂H₄O₂ there are 2 Carbon atoms, 4 Hydrogen atoms and 2 Oxygen atoms.