Choose the grammatically correct sentence:

The correct answer is Option (1) → Hardly had I boarded the metro at Kashmere Gate when I noticed that my bag was still on the platform.

“Hardly had ... when”:

• “Hardly” here means “only just”. It shows that one action happened right after another.
• When a sentence starts with “Hardly”, the helping verb comes before the subject: Hardly had I boarded.
• The second part then begins with when.

Why the Other Options are Incorrect?

Option 2: Hardly had I boarded the metro at Kashmere Gate than I noticed that my bag was still on the platform. — Incorrect. “Hardly had” is followed by “when”, not “than”.

Option 3: Hardly I had boarded the metro at Kashmere Gate when I noticed that my bag was still on the platform. — Incorrect. After “Hardly” at the start, the helping verb “had” must come before the subject “I”.

Option 4: Hardly had I boarded the metro at Kashmere Gate then I noticed that my bag was still on the platform. — Incorrect. “Then” means “after that”. It cannot join the second part to “Hardly had”.