Why is the chemical formula for water `H_2O` and for sodium chloride NaCl, why not `HO_2` and `NaCl_2`?

Write the chemical formulae of the following: sodium chloride

The formula unit of H_(2)O is

Why SiO_2 does not dissolve in water ?

Mention the number of sodium and chloride ions in each unit cell of NaCl

We write symbol of water as H_2O . State why should not we write it HO2' .

Anitha wrote the formula for oxygen molecule as 2O. Is it correct or not? Why?

Why SiO_(2) does not dissolve in water.

Write a balanced chemical equation with state symbols for the following reactions. (i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride. (ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.

Sodium catches fire in water. Why?