Explanation:

Correct Answer is (b).The original sentence is erroneous.
Reason: The sentence is in simple past. So the simple past form of the verb ‘attack’ should be used. Moreover, prepositions are not used with transitive verbs. ‘Attacked’ is a transitive verb in this sentence and should not be followed by the preposition ‘on’. Hence, ‘attacked’ should be used in place of ‘attacking’ and ‘on’ should be omitted in order to make the sentence grammatically correct.
Among the given choices, only option B replaces the given bold part most appropriately.
The sentence after replacement becomes:
The special task force attacked the terrorists and successfully captured their leader.Option B is hence the correct answer.