Final answer:
The correct passive form of the sentence "Who killed the chicken?" is "Who was the chicken killed by?". This conversion to passive voice moves the focus from the subject to the object of the sentence, using a form of 'be' and the past participle of the verb.
Step-by-step explanation:
In English grammar, switching from active voice to passive voice involves changing the focus of the sentence from the doer of the action (the subject) to the recipient of the action (the object). To form the passive voice, a form of the verb 'be' is used together with the past participle of the main verb. Along with this, the preposition 'by' can be used to introduce the doer of the action.
Given the sentence "Who killed the chicken?", the correct passive form would be: "Who was the chicken killed by?" Here, 'was' is the form of the verb 'be' in the past tense, 'killed' is the past participle of the verb 'kill', and the phrase 'by whom' (which is implicitly there) completes the passive construction, although in common usage, particularly in questions, it may be omitted or placed at the beginning of the sentence.
The active and passive voice serve different purposes in communication. The active voice emphasizes the action and its doer, while the passive voice shifts the focus to the recipient of the action. This distinction can affect the clarity and impact of our statements. The passive voice is often used when the doer is unknown, unimportant, or implied within the context.