Which region is most densely populated?

The correct answer is Option (2) → Indonesia

Indonesia has a very large population, and its island of Java is one of the most densely populated areas of the world. Greenland and Siberia are very cold, and Western Australia is mostly dry, so very few people live there.

Note: This question is not from NCERT. NTA does this once in a while, but such questions are very few. Your NCERT is still enough.