Answer:
D
Step-by-step explanation:
Ketones are a class of organic compounds that have an Oxygen double bonded to the middle of the main carbon chain.
Option A is not a ketone (despite having an Oxygen double bonded to the middle of the main carbon chain) because it has an adjacent single bonded Oxygen in the main carbon chain. This type of compound is classified as an "Ester".
Option B is not a ketone, but is instead classified as an aldehyde, a group of compounds with their Oxygen double bonded at the end of the main carbon chain.
Option C is not a ketone (despite having an Oxygen double bonded to the middle of the main carbon chain), but is instead classified as an Carboxylic Acid, because it has an adjacent single bonded Oxygen in the main carbon chain, and both of these pieces (with the single bonded O pointing outward) are at the end of the main carbon chain.
Option D is a ketone because it does have an Oxygen double bonded somewhere to the middle of main carbon chain, not at an end, and not with another Oxygen single bonded adjacently in the carbon chain. Specifically, this ketone is "2-pentanone" or "methyl propyl ketone"