The correct answer is: E. No error
The sentence “Hardly had I entered the compartment than I met my friend Vishwas” is grammatically correct. It uses the past perfect tense to describe an event that happened before another event in the past. The past perfect tense is formed with the past participle of the verb (in this case, “entered”) and the auxiliary verb “had.” The sentence also uses the subordinating conjunction “than” to introduce the second event, which happened immediately after the first event.
The other options are incorrect because they either change the meaning of the sentence or make it grammatically incorrect. Option A, “Hardly had I,” changes the meaning of the sentence by making it sound like the speaker was not sure whether or not they had entered the compartment. Option B, “entered the compartment,” is grammatically incorrect because it does not use the past perfect tense. Option C, “than I met,” is grammatically incorrect because it does not use the subordinating conjunction “than.” Option D, “my friend Vishwas,” is grammatically correct, but it does not make sense in the context of the sentence.