Choose the grammatically correct sentence:

The correct answer is Option (1) → My sister thinks that cooking for ten guests is easier than cleaning up after them.

Two actions compared with “than”:

• When two actions are compared with “than” or “as”, both must be in the same form.
• Here both actions are -ing forms: cooking ... than cleaning up.

Why the Other Options are Incorrect?

Option 2: The librarian suggested me a good book on Indian birds. — Incorrect. The option says “suggested me a good book”. “Suggest” takes the thing as its object, and the person comes after “to”.
Corrected: The librarian suggested a good book on Indian birds to me.

Option 3: At no time the guard left the gate during the night. — Incorrect. The option says “At no time the guard left”. When a sentence starts with “At no time”, the helping verb comes before the subject.
Corrected: At no time did the guard leave the gate during the night.

Option 4: Because the power had gone off in the whole colony during the cricket final. — Incorrect. The option is only a “because” part. It gives a reason but has no main part to tell what happened.
Corrected: Because the power had gone off in the whole colony, we missed the end of the cricket final.