Which class of organic compound is least likely to be used as an organic solvent? aldehyde ketone alkyl halide ether

 Aldehyde

Explanation:   The important property of any kind of solvent is to facilitate the mixing of reagents present in the reaction mixture and to mediate the proton transfer. Thus out of aldehyde, ketone, alkyl halide and ether, Aldehyde can be considered as the least used organic solvent.

Aldehyde is highly reactive in nature due to less steric hinderance unlike ketone which has hydrocarbon chain on the both sides of the carbonyl group.

Ether is a polar compound which is mostly used as the organic solvents like diethyl ether, tetrahydrofuran etc.

Some of the Ketones which are used as solvents re acetone, DMSO etc.

Alkyl halide like chloroform, dimethyl dichloride are also used as organic solvents.

The structure of each of the kind of solvent is attached in the image below -