Ans: A) HCl
Neutralization reaction is one where an acid reacts with a base to form salt and water.
The given reaction is;
HCl + NaOH → NaCl + H2O
In general, an acid is the species which loses a proton i.e. H+ ion. Whereas base accepts a proton. Therefore the molecule where the proton count or the number of hydrogens decreases as the reaction proceeds can be identified as an acid.
Here, as the reaction progresses, HCl loses its hydrogen hence HCl is an acid i.e. hydrochloric acid.
NaOH, sodium hydroxide is a base
NaCl, sodium chloride is a salt.