Correct Answer: Imperative

Solution : The first option is correct.

Obligation is the state of having to do something because it is a law or duty, or because you have promised. Imperative denotes something very important or urgent, making it a fitting synonym.

The meanings of the other options are as follows:

Loophole: It denotes a way of avoiding something because the words of a rule or law are badly chosen.

Discharge: It means allowing somebody officially to leave; to send somebody away.

Quietus: It is a final settlement (as of a debt) or removal from activity, especially death.