Synonyms

Noisome means something that is extremely offensive or disgusting, particularly to the sense of smell. The other options (pleasant, mannerly, distinguished, orderly) are all positive qualities that are opposites of the actual meaning.

A nostrum is a medicine, especially one that is not effective or is questionable, often associated with quacks. Quack remedy precisely captures this meaning of a dubious or fake cure.

Nugatory means something that is trifling, useless, or of no value. Invalid is the closest match among the options, as both suggest something lacking validity or importance.

Noxious means something harmful, poisonous, or very unpleasant. Pernicious similarly means having a harmful effect, especially in a gradual or subtle way. The other options are all positive or neutral terms.

Oblique means something that is neither perpendicular nor parallel, typically at a sloping angle. Slanting directly captures this meaning of being at an angle rather than straight or normal.

Obsequious describes someone who is obedient or attentive to an excessive or servile degree. Submissive captures this trait of being overly compliant or eager to please, especially those in authority.

Obstreperous describes someone who is noisy, difficult, or unruly in their behavior. Unruly is the perfect match as it specifically means difficult to control or discipline.

To obtrude means to become noticeable in an unwelcome or intrusive way, or to force something upon someone's attention. Appear unwelcome captures this sense of imposition or intrusion.

Odious describes something that is extremely unpleasant, repulsive, or deserving hatred. Hateful directly expresses this strong negative quality that arouses intense dislike or disgust.

Obviate means to do away with or prevent. So option 4 is correct.  

Obtrusive describes something that is noticeable or prominent in an intrusive or unwelcome way. Prominent captures this quality of standing out or being easily noticed, even if the connotation is slightly different.

Obdurate describes someone who is stubbornly persistent in wrongdoing or refuses to change their opinion or course of action. Stubborn perfectly captures this quality of being unreasonably unyielding or refusing to change.

Odium means general hatred, disgust, or public condemnation. Disgust directly corresponds to this meaning as a strong feeling of revulsion or intense dislike. The other options (Delight, Approval, Pleasure, Grace) are all positive emotions, opposite in meaning to odium.

Ominous means suggesting that something bad or unpleasant is about to happen; threatening or portending evil. Threatening (option D) is the correct synonym as it directly captures this sense of danger or impending harm. The other options (Promising, Cheery, Encouraging) all have positive connotations opposite to ominous.

Officious means excessively willing to offer advice or interfere; meddlesome or intrusive in an overbearing way. Interfering (option B) correctly captures this meaning of unwanted, intrusive involvement. Submissive means yielding, while Obstructive means blocking - neither captures the specific intrusive nature of officious.