Antonyms

Hubbub means noise, uproar, or confused activity. Silence is the direct opposite - complete absence of sound or activity. The other options (blatant, uproar, notice) are synonyms or related terms, not antonyms.

Imperative means absolutely necessary, urgent, or of vital importance. Trivial means unimportant, insignificant, or of little value - directly opposite in meaning. The other options (fickle, fumble, frown) are unrelated to the concept of necessity.

Incite means to stir up, provoke, or encourage (often negative actions like violence or trouble). Pacify means to calm, soothe, or bring peace - directly opposite in effect. The other options (rage, poor, lift) are not valid antonyms.

Imbecile refers to a foolish or stupid person. Genius refers to an exceptionally intelligent or talented person - the direct opposite in terms of mental capacity. The other options (reality, cruel, filthy) are unrelated to intelligence.

Indigent means poor, needy, or lacking basic resources. Rich means wealthy or having abundant resources - the direct opposite in economic status. The other options (hide, frown, crown) are unrelated to poverty or wealth.

Inept means incompetent, unskilled, or lacking ability. Adept means skilled, proficient, or competent - the direct opposite in terms of capability. The other options (adapt, cringe, robust) are not valid antonyms.

Increment means an increase or addition in amount or degree. Curtailment means reduction, limitation, or cutting back - the direct opposite in terms of growth. The other options (hide, diligence, exonerate) are not antonyms.

Indictment is a formal charge or accusation of a serious crime. Pardon means forgiveness, release from punishment, or absolution - conceptually opposite as it frees someone rather than accusing them. Acquit (option D) is similar but pardon is the stronger opposite to indictment.

Industrious means diligent, hardworking, or characterized by steady effort. Indolent means lazy, idle, or averse to work - the direct opposite in attitude toward effort. The other options (fame, rotten, decorum) are unrelated.

Confess means to own or admit as true. Deny means to state that (something declared or believed to be true) is not true.

 Something that is ideal is considered perfect. Hence, imperfect is opposite in meaning.

Agnostic means a person who holds that the existence of the ultimate cause and the essential nature of things are unknown and unknowable or that human knowledge is limited to experience. It is the best option here. So, it is the correct answer.

All the other options except costly are similar in meaning to cheap.

The correct option is (3).

  The correct option is option 3 as opposite of Optional is Compulsary .