Which of the following country's population does not have triangular shaped age-sex pyramid?

Australia

The correct answer is Option (1) - Australia

The age-sex pyramid of Nigeria, Bangladesh and Mexico is a triangular shaped pyramid with a wide base and is typical of less developed countries. These have larger populations in lower age groups due to high birth rates.

Australia’s age-sex pyramid is bell shaped and tapered towards the top. This shows birth and death rates are almost equal leading to a near constant population.

NOTE: This question is from pre rationalised syllabus.