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

Propionic acid is the main byproduct of the treatment of 1, 1, 1-trichloropropane with aqueous potassium hydroxide.
Alc. KOH leads to substitution while aq. KOH causes elimination in the haloalkane molecule generally. Since aq. KOH is being utilised here, a substitution reaction is most advantageous.
The preferred response would be:

On a carbon atom, there cannot be more than one OH group. A water molecule will be easily lost by the chemical in this scenario, making a more stable aldehyde, ketone, or carboxylic acid.

$(\mathrm{HO}{)}_3{\mathrm{CCH}}_2{\mathrm{CH}}_3\to (\mathrm{HO}){\mathrm{COCH}}_2{\mathrm{CH}}_3+{\mathrm{H}}_2\mathrm{O}$.