Statement (A): ${\text{N}}_{\text{2}}{\text{O,\hspace{0.17em}N}}_{\text{2}}{\text{O}}_{\text{3}}{\text{,\hspace{0.17em}N}}_{\text{2}}{\text{O}}_{\text{4}}$  molecules will follow law of multiple proportions.

Statement (B): ${\text{H}}_{2\left(g\right)}+\text{C}{l}_{\text{2(g)}}\to \text{2HC}{l}_{\text{(g)}}$will follow Gay- Lussac’s Law of combining volumes.

Statement (C):$\text{Na}+\text{HC}l\to \text{NaC}l+\text{H}$ is Atomic equation.

Law of multiple proportions: Different weights of an element that combine with a fixed weight of the other element bear a simple numerical ratio.

Ex: Oxides of Nitrogen ${\text{N}}_{\text{2}}{\text{O,\hspace{0.17em}N}}_{\text{2}}{\text{O}}_{\text{3}}{\text{,\hspace{0.17em}N}}_{\text{2}}{\text{O}}_{\text{4}}$ .

Gay- Lussac’s Law of combining volumes: When gases react, the volumes of the reactants and products are in the ration of small whole numbers provided the volumes are measured at the same temperature and pressure.

Ex: 1 volume of Hydrogen + 1 volume of Chlorine $\to$  2 volumes of Hydrogen Chloride ${\text{H}}_{2\left(g\right)}+\text{C}{l}_{\text{2(g)}}\to \text{2HC}{l}_{\text{(g)}}$

The combining ration is  1:1:2

Atomic Equation: A balanced equation in which the elementary substances are expressed in the atomic form in atomic equation.

Ex:  $\text{Na}+\text{HC}l\to \text{NaC}l+\text{H}$