"Authoritative" and "official" are synonyms. They refer to an object's standing or reputation as being of the highest official or institutional caliber. The other words might appear similar but do not have closely related meanings. "Authorial" refers to the something (usually intention) pertaining to an author.

"Enigmatic" and "mystical" are synonyms describing the quality of something esoteric and puzzling. The other words do not have meanings related to this sense of mystery. "Magnetic" refers either to the quality (in a person) of having a compelling personality, or the physical quality of attracting metals containing an opposite pole. "Magnificent" is an extremely positive adjective. "Magnanimous" refers to the quality of being generous and sympathetic to others.

"Unadulterated" refers to something that is pure; something that has not been tampered with. The other answer choices have similarly positive connotations but don't quite capture this shade of meaning. "Elegant" may refer to something luxurious, while "special" and "top-notch" refer to something of good quality. "Considerate" is not at all related to the word "unadulterated."

The adjective "inane" means pointless, silly, and foolish. This is closest in meaning to "fatuous" which means vacuous, without purpose. Additionally, "ponderous" means slow-moving; "truculent" means aggressive, hostile, eager to fight; "ingenuous" means naive, innocent, gullible; "disingenuous" means false, deceptive, insincere.

The adjective "paramount" means of particular importance, especially "important." Additionally, "inveterate" means (of behavior) entrenched and habitual; "invalid" means not valid, not acceptable; "implied" means hinted at, suggested; an "ingrate" is an ungrateful and rude person.

The adjective "indubitable" means not able to be doubted, unquestionable, or "certain." Additionally, "exasperated" means deeply frustrated and annoyed by; "unctuous" means exceedingly obsequious and fawning, prone to excessive flattery and sycophantic behavior; "quiescent" means at rest, inactive, dormant.

The adjective "overt" means obvious, easily noticeable, not well-concealed, conspicuous. Additionally, "lambent" means flickering; "exhaustive" means including all possible considerations, comprehensive; "factious" means prone to, or likely to, cause disagreement; "ebullient" means overly enthusiastic. 

The adjective "cogent" means (of an argument) convincing, compelling and well-reasoned. Additionally, "introspective" means inwardly thoughtful; "limpid" means clear; "bestial" means savage (like a beast); "incumbent" means required, very important in order to get something done.

"Arbitrary" means random and meaningless, not based on any criteria. Additionally, "susceptible" means vulnerable to, likely to be harmed by; "capacious" means roomy, having lots of space; "awry" means 'out of place,' amiss, gone wrong; "fraudulent" means not genuine, not authentic.

The adjective "cognizant" means aware of. Additionally, "ominous" means suggesting something bad will happen, portentous, threatening; "deleterious" means causing harm, injurious.