Which of the following groups have an activating effect on the benzene ring?
$-OH, -COCH_3, -NO_2, -NH_2, -Cl, -Br, -NHCOCH_3, -COOH$

(A) Groups that increase the electron density of the benzene ring through resonance ($+R$ or $+M$ effect) are known as activating groups.
Among the given groups,$-OH$,$-NH_2$,and $-NHCOCH_3$ are activating groups because they donate electron density to the ring via their lone pairs.
Therefore,the activating groups are: $-OH, -NH_2, -NHCOCH_3$.