Give three kinds of information conveyed by the formula $H_{2}O.$

Information conveyed :
1. $H_{2}O$ is the chemical formula of water.

2. There are 2 atoms of hydrogen and one atom of oxygen.
3. The definite proportion: 2 grams of hydrogen and 16 grams of oxygen. It means the hydrogen and oxygen combine together in the ratio 1:8.
4. The law of mass conservation: The mass of the products in a chemical reaction must equal the mass of the reactants.

$\underset{4+32=36g}{\underset{4g}{2H_2}+\underset{32g}{O_2}}\to \underset{2\times 18=36g}{2H_{2}O}$