The correct answer is: B. He was given a reward by the king.
The sentence “The king gave him a reward” is in the active voice. In the active voice, the subject of the sentence performs the action. In this case, the subject is “the king” and the action is “gave.” The direct object of the sentence is “him” and the indirect object is “a reward.”
The passive voice is formed by using the verb “to be” and the past participle of the main verb. In this case, the sentence would be “He was given a reward by the king.” In the passive voice, the subject of the sentence receives the action. In this case, the subject is “he” and the action is “was given.” The direct object of the sentence is still “a reward” but the indirect object is now “the king.”
The other options are incorrect because they are not in the passive voice. Option A, “He was given by the king a reward,” is incorrect because it uses the preposition “by” instead of the verb “to be.” Option C, “He were given a reward by the king,” is incorrect because it uses the wrong verb tense. Option D, “A reward was given by him to the king,” is incorrect because it changes the order of the subject and the direct object.