The major product formed when 1, 1, 1-trichloro-propane is treated with aqueous potassium hydroxide is propionic acid.

Alc. KOH causes elimination in the molecule of haloalkane generally, while aq. KOH leads to substitution. Here aqueous KOH is used, substitution reaction is most preferable.

The initial reaction is the nucleophilic substitution, which will form a trihydroxy compound, since, three hydroxy group on one carbon is unstable and result in dehydration and form carboxylic acid.