"Optimal" is an adjective describing a noun that is the best or as well-suited to something as can be. Of the answer choices, "ideal" has the closest meaning. 

“Ramshackle” means in very poor condition, so we need to pick out an answer choice that means in disrepair. That means that “pristine” cannot be the correct answer, because “pristine” is an adjective that can mean, spotless, perfect, or in something's original condition making it an antonym, not a synonym, of “ramshackle.” “Dilapidated,” however, is an adjective that is used of a building or object and means in disrepair, and because “dilapidated” is the answer choice closest in meaning to “ramshackle,” “dilapidated” is the correct answer.

"Impeccable" means flawless, or "perfect."

"Hackneyed" means trite, unoriginal or old-fashioned, so "trite" is the correct answer. For clarification, "destitute" means very poor, "original" means first or authentic, "homeless" means not having a home, and "weird" means eerie or strange.

"Sublime" means perfect or awe-inspiring, so "magnificent," which means impressive, striking, or excellent, is the correct answer. For clarification, "paltry" means meager, "noxious" means toxic or poisonous, "absolution" means forgiveness, and "denigrate" means belittle or criticize.

"Insipid" is an adjective that means "tasteless, flavorless, or bland" when referring to food or drink, and "unimaginative, drab, or tedious" when referring to writing, art, or ideas. While "ennui" might look like a good candidate for a synonym of "insipid," ennui is a noun that means "a feeling of listlessness and dissatisfaction arising from a lack of occupation or excitement," and while something that is insipid might cause a state of ennui, "ennui" is a noun and "insipid" an adjective, so "ennui" cannot be the correct answer. "Humdrum," however, can be used as an adjective meaning "lacking excitement or variety; dull; monotonous." Because "humdrum" is the answer choice closest in meaning to "insipid," "humdrum" is the correct answer.

"Glorious" means wonderful, or having glory.

"Mediocre" means common or ordinary, so "ordinary" is the correct answer.

"Meager" is an adjective that describes a very small amount. For example, "His meager meal included one piece of bread and a small cup of milk." If something is "scarce,' it is not abundant. These two words are very similar. "Ample" is an antonym to "meager."

"Profuse" is an adjective that means "abundant" or plentiful.

"Infinite" means limitless, or impossible to measure or calculate. "Substantial" means important, large, or valuable. "Benign" means gentle or kind, and in medical terms means not harmful. "Sparse" is an antonym of "profuse" and means few or infrequent.