Why did pouched mammals survive in Australia?

The correct answer is Option (2) → They had no competition from other mammals

Continental drift moved land masses and brought groups of mammals together or kept them apart. Where mammals met stronger competitors they were replaced, and where they were cut off they survived.

Option (1) They were better adapted to the climate — Incorrect. NCERT does not give the climate as the reason. The book links their survival to the absence of rivals, not to a special fit with the Australian climate.

Option (2) They had no competition from other mammals — Correct. Continental drift kept Australia apart, so the pouched mammals (marsupials) there met no competition from any other mammal and survived.

Option (3) They were more intelligent — Incorrect. Intelligence is mentioned for mammals as a whole, which were better than reptiles at sensing and avoiding danger. It is not the reason given for the survival of pouched mammals in Australia.

Option (4) They had a varied diet — Incorrect. NCERT says nothing about the diet of these animals as a reason for their survival. Their survival is explained by isolation and lack of competition.

NCERT Extract:
A Brief Account of Evolution – “… Mammals were more intelligent in sensing and avoiding danger at least. When reptiles came down mammals took over this earth. There were in South America mammals resembling horse, hippopotamus, bear, rabbit, etc. Due to continental drift, when South America joined North America, these animals were overridden by North American fauna. Due to the same continental drift pouched mammals of Australia survived because of lack of competition from any other mammal.”