The correct Active/Passive form of the given sentence is:

☀ The food was being cooked by him last night.

So, the correct passive form is: "The food was being cooked by him last night."

The other options and their explanations:

☀ The last night food was cooked by him.

• This option is grammatically correct in the passive voice, but it rearranges the sentence by placing "last night" before "food," which sounds awkward and less natural.

☀ The last night food were being cooked by him.

• This option contains a grammatical error. The subject "food" is singular, so it should be "was" instead of "were" when using the past continuous tense.

☀ The food had been cooked by him last night.

• This option uses the past perfect tense ("had been cooked") instead of the past continuous tense used in the original sentence. The meaning is slightly different, as the past perfect suggests that the cooking was completed before another past event, while the past continuous conveys an ongoing action in the past.