If this sentence is changed to active voice, then the subject is also changed, in order to retain the meaning of the sentence.

So, the object takes the place of the subject and vice versa and the word 'by' is removed as now the subject performs the action against the object. The verb form of the sentence is also changed from passive form to active.

'Subject (He) + verb (was congratulated) + by + object (his teacher) + prepositional phrase (for his brilliant success in the recent examination)' changes to:

'New subject (His teacher) + verb (congratulated) + new object (him) + prepositional phrase'

The active form of 'was congratulated' in the simple past tense is 'congratulated'.

This can be seen in option B, hence it's the right answer.

Option A: The subject and object have not been changed, but the verb has changed from passive to active. As a result, the meaning of the sentence has changed.

Option C: The tense of the sentence has changed from past 'was congratulated' to future 'will congratulate'. The meaning has hence changed.

Option D: The prepositional phrase 'for his brilliant success' is missing.