Antonyms

The opposite of phlegmatic, among the choices for this question, is vivacious, meaning active; vigorous; energetic; brisk.

Obstreperous means unruly; disorderly; boisterous. Its opposite is easy to control.

Occult means mysterious; enigmatic. Its opposite is readily fathomable.

Opaqueness means obscurity; lack of clarity. Its opposite is clarity, meaning transparency.

Onerous means demanding; exacting; tiresome. Its opposite is requiring little effort.

Nascent means just come into being; incipient. Its opposite is fully established.

The intended antonym is 'cheap' as something with low monetary value. However, 'worthless' would be more precise. 'Expensive' is actually a synonym of valuable. 'Unvaluable' is not a standard word, and 'non-valuble' is both misspelled ('valuable') and not standard. The question tests basic opposites in the context of monetary worth.

Prolix means using too many words; tediously long or verbose. Terse means brief and to the point; concise. They describe opposite styles of communication.

Omniscient means knowing everything; all-knowing. Ignorant means lacking knowledge or awareness. The terms represent opposite states of knowledge.

Vapid means lacking liveliness, interest, or flavor; dull or tedious. Spirited means full of energy, enthusiasm, or animation. They describe opposite levels of vitality.

Prodigious means extraordinarily large or impressive in scale, amount, or degree. Minute means extremely small or tiny. They describe opposite magnitudes.

Compendious means concise or expressing much in few words. Verbose means using more words than needed, making it the direct antonym.

Avid means showing enthusiasm or eagerness. Loath means reluctant or unwilling, making it the direct antonym.

Fortuitous means happening by chance or accident. Designed means planned or intentional, the opposite of accidental.