The correct passive form of the given sentence is:

☀ Not a word was spoken by the criminal in self-defense.

 Let's break down the options:

1. Not a word was spoken by the criminal in self-defense. (Correct) This sentence correctly uses the passive voice and conveys the same meaning as the original sentence.

2. The criminal spoke not a word in self-defense. (Incorrect) This option is in the active voice, not the passive voice. It represents the same meaning as the original sentence but doesn't use the passive construction as required.

3. The criminal in self-defense spoke no word. (Incorrect) This option is in the active voice and changes the word order from the original sentence. The correct passive form should maintain the word order of the original active sentence.

4. The criminal spoke in self-defense not a word. (Incorrect) This option is in the active voice and changes the word order from the original sentence. It also introduces an adverbial phrase "in self-defense," which modifies "spoke," but it is not part of the passive construction. The correct passive form should maintain the word order of the original active sentence and include the agent using "by."