Select the most appropriate option to improve the bold part of the sentence.
Hardly he had reached the station when the train left.

Correct option is B

The correct substitution of the highlighted words is (b) Hardly had he reached.
Explanation: After negative/limiting adverbs like Hardly, Scarcely, Rarely, we use inversion in formal English: Adverb + auxiliary + subject + main verb. With past perfect, the auxiliary is had. The clause then typically takes when to introduce the second event.
Grammatical rule used:
· Hardly/Scarcely had + subject + V³ + when + past simple
· No sooner had + subject + V³ + than + past simple (parallel construction)
· Example: Hardly had I sat down when the bell rang. / No sooner had he arrived than it started raining.
· Information booster / exceptions:
· Do not use “Hardly he had…” (no inversion).
· With No sooner, pair with than, not when.
Why others are wrong:
· (a) He had hardly reached… — no inversion after Hardly at clause-initial position.
· (c) requires than (not given), and also needs inversion: No sooner had he reached than…
· (d) incorrect word order for inversion.