Which of the following alkene on reductive ozonolysis gives ketones only as the product?

Reductive ozonolysis of an alkene involves the cleavage of the carbon-carbon double bond ($C=C$) to form carbonyl compounds. If the carbons involved in the double bond are substituted with two alkyl groups (i.e., tetrasubstituted or trisubstituted with alkyl groups), the products are ketones. If one or both carbons are bonded to a hydrogen atom, the products are aldehydes.

Analyzing the options:

But-2-ene ($CH_3-CH=CH-CH_3$): Each carbon of the double bond is bonded to one hydrogen atom. Ozonolysis yields two molecules of acetaldehyde ($CH_3CHO$), which are aldehydes.

1,2-butadiene ($CH_2=C=CH-CH_3$): This is an allene. Ozonolysis yields formaldehyde ($HCHO$), carbon dioxide ($CO_2$), and acetaldehyde ($CH_3CHO$).

1,4-cyclohexadiene: The double bonds are within the ring. Ozonolysis leads to the formation of dialdehydes (specifically, succinaldehyde).

2,3-dimethylbut-2-ene ($(CH_3)_2C=C(CH_3)_2$): Each carbon of the double bond is bonded to two methyl groups. Ozonolysis cleaves the double bond to produce two molecules of acetone ($(CH_3)_2C=O$), which is a ketone.

Answer: 2, 3-dimethylbut-2-ene