Identify the correct Passive Voice form of the following sentence.

Who did this?

By whom was this done?

The correct answer is Option (3) → By whom was this done?

To convert a sentence from active to passive voice, we need to:
1. Make the object of the active voice sentence the subject of the passive voice sentence.
2. Change the verb to the past participle form.
3. Add the helping verb "was" or "were" before the past participle.
4. Add the preposition "by" before the subject of the active voice sentence.

In the example sentence, the object is "this" and the subject is implied to be the person who did the action. So, to convert the sentence to passive voice, we make "this" the subject and change the verb "did" to the past participle form "done." We then add the helping verb "was" and the preposition "by" before the implied subject, which is "the person who did the action."

Therefore, the correct passive voice form of the sentence "Who did this?" is By whom was this done?