The correct passive form of the given sentence is:

☀ The bell was not rung by him.

Let's break down the options:

1. The bell was not rung by him. (Correct) This sentence correctly uses the passive voice and conveys the same meaning as the original sentence.

2. The bell is not rung by him. (Incorrect) This sentence is in the passive voice, but it implies a general statement about who rings the bell, not specifically referring to the action in the past as in the original sentence.

3. The bell has not been rung by him. (Incorrect) This sentence uses the present perfect tense ("has not been rung"), which is not the appropriate tense to match the past action indicated in the original sentence.

4. The bell had not been rung by him. (Incorrect) This sentence uses the past perfect tense ("had not been rung"), which is also not the appropriate tense for the same reason as option 3. The past perfect tense indicates an action completed before another past action, which is not applicable here.