Which of the following substances could the unknown be: KOH, NH3, HNO3, KClO2, H3PO3, CH3COCH3 (acetone) ?

CH3COCH3

Explanation:

Acetone is an organic compound belonging to the organic ketone function.

To recognize which function a compound belongs to, we must analyze its functional group. For example, hydroxyl (OH) is characteristic of alcohols. For ketones, the functional group is carbonyl, which is represented below.

Analyzing the options, we can notice that NH3, HNO3, KClO2 and H3PO3 are inorganic compunds, because they don't have carbon in their structures. KOH has the hydroxyl, so it's a alchol, and CH3COCH3 may be writing as a ketone.