Choose the grammatically correct sentence:

The correct answer is Option (4) → The bank officer explained the new loan rules to my father.

“Explain” + thing + “to” + person:

• “Explain” cannot take the person straight after it. We do not say “explained my father the rules”.
• The thing explained comes first, and the person comes after “to”: “explained the new loan rules to my father”.

Why the Other Options are Incorrect?

Option 1: Cooking at home is healthier than to order food online. — Incorrect. The two things compared must be in the same form. “Cooking” is an -ing form, so the second one must be “ordering”.
Corrected: Cooking at home is healthier than ordering food online.

Option 2: Didi wants to try new something for her birthday dinner. — Incorrect. An adjective comes after “something”, not before it.
Corrected: Didi wants to try something new for her birthday dinner.

Option 3: Raj has finished his science project, and so I have. — Incorrect. After “so” in a short addition, the helping verb comes before the subject.
Corrected: Raj has finished his science project, and so have I.