The following compound can be identified as

3: Lactone

Explanation:

Lactones are defined as carboxylic esters that contain the structure (−C(=O)−O−) which is essentially showing that an ester has now become part of the chemical structure of the ring.

Thus, looking at the question, it has the structure as defined in Lactones.

Thus, we can say that the compound is a Lactone.

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