If the earth's direction of rotation is reversed, what should be the IST when it is noon at the International Date Line?

Answer: (c) 18.30 hrs

With reversed rotation India (97.5° west of 180°) would be 6 h 30 min ahead: 18:30.

The idea

Longitude gives the size of a local-time difference, while the direction of rotation gives its sign. Reversing Earth’s spin reverses which side is ahead. Use the angular gap between the standard meridian and the meridian treated as the date line in the question.

Take 180° as the question’s date-line meridian → Subtract the IST meridian of 82.5°E → Obtain a 97.5° separation → Divide by 15° per hour → Reverse the usual ahead/behind relationship → Add 6.5 hours to noon

Why the others are wrong

(a) Neither normal nor reversed rotation gives 06:30.

(b) 05:30 is the answer with NORMAL rotation.

The trap

(b) is the normal-rotation answer — the question flips it.

Elimination technique

India lies west of the 180° meridian. With the spin reversed, its local time must be ahead of noon, so remove the morning options before calculating the 6.5-hour gap.

Also know

Rotation produces the daily cycle; revolution is Earth’s yearly journey around the Sun. The real date line bends around territories rather than following 180° everywhere. This hypothetical question uses the simple longitude-time model, not a proposed new civil time-zone system.