Which of the following sentences uses a modal wrongly?

The correct answer is Option (2) → Those clouds look heavy, Manoj. You had better took your raincoat to the fields.

Had better is followed by the base verb:

• The given sentence says “had better took”.
• Had better gives strong advice about now or the future. It is always followed by the base verb (the simple form of the verb, like go, eat).
• Here the past form “took” is used, so the sentence is wrong.
• Corrected: Those clouds look heavy, Manoj. You had better take your raincoat to the fields.

Why the Other Options are Incorrect?

Option 1: Might I use your charger for a few minutes? This sentence is correct. “Might I” is a very polite way to ask for permission.

Option 3: Dadi would rather not eat out during Navratri. This sentence is correct. “Would rather not” + base verb shows what a person prefers not to do.

Option 4: The film must have started by now. We are twenty minutes late. This sentence is correct. “Must have” + past participle (V3) shows a confident guess about the past.