Select the option that is the most appropriate antonym of the highlighted word…

Concept: An antonym must sit at the opposite end of the same semantic dimension as the given word — it is not enough for it to be a different or unrelated adjective. Adjectives that describe how a message is conveyed run along a single axis: at one end the meaning is stated openly and in full, and at the other end it is left for the listener to infer. A word drawn from a different axis, such as the quantity of information supplied, the significance of a thing, or its fragility, can never be the antonym, however different from the given word it may feel.

Application: In this sentence, explicit describes instructions that state everything openly and leave nothing to be worked out, which is exactly why they are easy to follow. Moving to the opposite end of that same stated-versus-inferred axis gives implicit — meaning that is suggested or understood without being put into words. Implicit is therefore the most appropriate antonym of explicit.

Contrast: the remaining choices each belong to a different semantic axis:

• detailed — the quantity-of-information axis. A message can be long and richly detailed and still leave its real point unstated, so detailed neither matches nor reverses openness of expression.

• important — the significance axis. It reports how much a thing matters and says nothing at all about whether its meaning is spelled out or left implied.

• delicate — the fragility-and-care axis. It reports how easily something is damaged or how carefully it must be handled, which is again unrelated to openness of expression.

Cross-check: substitute each candidate back into the sentence. "The instructions were implicit" reverses the original sense — the instructions would now leave things unsaid, so the clause "and easy to follow" no longer sits comfortably with them, which is the signature of a true opposite. Each of the other substitutions changes the topic of the description instead of reversing it. That substitution test is the reliable way to separate a genuine antonym from a merely unrelated adjective.