The correct passive form of the given sentence is:

☀ Mohan was elected captain by the boys.

Let's break down the options:

1. The boys were elected captain by Mohan. (Correct) This sentence correctly uses the passive voice and conveys the same meaning as the original sentence. It places the focus on the boys as the ones who performed the action of electing Mohan as captain.

2. Mohan is elected captain by the boys. (Incorrect) This option uses the present tense "is elected," which is not consistent with the past tense of the original sentence. The correct form should use the past tense "was elected," as shown in option 1.

3. Mohan was elected captain by the boys. (Correct) This option is identical to option 1 and correctly represents the passive form of the given sentence.

4. Mohan and the boys elected the captain. (Incorrect) This option is in the active voice and changes the roles of the subject and object from the original sentence. It does not represent the passive form of the sentence.