$\mathrm{Hydrogen}+\mathrm{Chlorine}\to \mathrm{Hydrochloric} \mathrm{acid}$

This is a:

We are able to comprehend and respond to the question by studying all of the aforementioned phenomena. Hydrochloric acid is created utilising hydrogen and chlorine in a number of processes. The term "photochemical reaction" refers to a reaction that takes place in the presence of light from the sun or another light source that gives the reactants photons.

In a hydrogen displacement reaction, an active metal takes the place of the acid's hydrogen. Certain metals have the reactivity to take the place of the hydrogen in water. Such a process yields metal hydroxide and hydrogen gas as its byproducts. This kind of reaction occurs with all group 1 metals (alkali metals).

When two or more elements or compounds combine to create a single product, the reaction is known as a direct combination reaction. Equations of the type X + Y → XY are used to depict these reactions. A combination reaction occurs when two or more components combine to produce a single compound.

This is known as a chemical combination reaction. Here two reactants hydrogen and chlorine combine to form hydrochloric acid.

Hence, option A is correct.