"Covert" is an adjective describing something that is secret, hidden, or undercover. "Open" can be an antonym to "covert" if used to describe someone's attitude towards information. None of the other words are particularly related to "covert."

Counterfeit is an adjective describing something that is fake, fraudulent, or unreal. "Counter-" is a prefix that connotes an opposite. "Valid" is close to an antonym to counterfeit.

"Noxious" means harmful or poisonous. A "noxious" gas might be toxic. "Hateful" means either deserving of or being filled with extreme anger. "Disruptive" means tending to disturb the normal order of a situation. "Exposed" refers to being uncovered or made visible.

The word "vacant" is related to the words "vacuum" and "vacation." A "vacuum" is an empty space. A vacation is "empty time" during which you can rest and do what you want to do. Whenever a piece of property is "vacant," it is empty, having nobody occupying it. We can also use the word "vacant" to describe something that is generally empty. Thus, a "vacant stare" is a facial expression that is "empty"—as though the person were looking off into space without any particular focus.

Whenever something is "stately," it is majestic or very grand. Things that are "important" can also be called "stately," but the two words are not exact synonyms. Instead, the best option for this question is the simple "impressive." Whenever something is "stately," its majesty and grandeur are impressive.

Inert is defined as "inactive" or "sluggish." Other answer choices are incorrect; iconic means relating to, or of the nature of an icon; "unwieldy" means cumbersome or unmanageable; "active" means energetic; and "intense" means extreme or passionate.

Whenever we deceive someone, we trick or lie to him or her.  Thus, something that is "deceptive" is something that we could call "tricky." A deceptive person is someone who manipulates with lies. A deceptive appearance is something that looks one way, though it really is not in fact that way. For example, a building might look deceptively tall when it is, in fact, quite short. Thus, it creates an illusion. This is why "illusory" is a good synonym for "deceptive."

"Insipid" means lacking interest or flavor, which is closest in meaning to "boring."

"Irate" is an verb that means "feeling or characterized by great anger." So, we need to pick out an answer choice that means something like "angry." "Furious" is an adjective that means either "extremely angry" or "full of anger or energy; violent or intense," and because it is the answer choice that is closest in meaning to "irate," "furious" is the correct answer.

"Glum" is an adjective that means "looking or feeling dejected; morose." So, we need to pick out a answer choice that means something like "morose." While "quiet" might look like a potentially correct answer because someone who is morose might also be quiet, "morose" does not mean the same thing as "quiet," so "quiet" cannot be the correct answer. "Melancholy," however, when used as an adjective, means either "having a feeling of melancholy; sad and pensive" or " causing or expressing sadness; depressing." Because "melancholy" is the answer choice closest in meaning to "glum," "melancholy" is the correct answer.