Such antimicrobials exhibit a range of cellular targets, the selective being the most effective against the widest range of microbes and the selective agents exhibiting specificity in terms of cellular targets and microbial types they are effective against.

least, most

Explanation:

Antimicrobials are substances that function by limiting the activities of microorganisms either by killing them or by inhibiting their growths.

Antimicrobials that exhibit a wide range of cellular targets are least selective of the type of cells they kill or inhibit. They are also said to have a wide spectrum of activities.

On the other hand, antimicrobials that exhibit a narrow range of cellular targets are most selective of the type of cells they kill or inhibit. They are said to have a narrow spectrum of activities.