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

The correct option is Australia.

An age-sex pyramid (or population pyramid) illustrates the distribution of various age groups in a population by sex. The shape of the pyramid reflects the demographic characteristics of a country:
1. Triangular-shaped pyramid: This shape is characteristic of expanding populations. It has a very wide base due to high birth rates and tapers rapidly toward the top due to high death rates in older age groups. Developing countries like Bangladesh, Nigeria, and Mexico typically exhibit this type of population structure.
2. Bell-shaped or rectangular/narrow-based pyramid: This shape is characteristic of stable or declining populations. It has a narrower base because of low or declining birth rates, and a relatively uniform width up to the older age groups due to high life expectancy and low death rates.

Australia is a developed nation with low birth rates and low death rates, resulting in a population pyramid that is column-like or bell-shaped rather than triangular. Therefore, Australia's population does not have a triangular-shaped age-sex pyramid.