A regressive population age structure is likely to be encountered in a country:

A regressive population age structure is characterized by a relatively high proportion of elderly people and a low proportion of young people. This can be caused by low birth rates, high death rates, and increased life expectancy.

Important Points

• A regressive population age structure is unlikely to be encountered in a country that has completed the demographic transition because in such countries, the population tends to have a more balanced age structure with a relatively smaller proportion of elderly people.
• A balanced population age structure with a relatively equal proportion of young and old population is not indicative of a regressive population age structure.
• A young population age structure is indicative of an expanding population, where there is a high proportion of young people and a low proportion of elderly people.
• A country in the early expanding stage of demographic transition is likely to have a young population age structure, not a regressive one.

Therefore, option 1 is the correct answer.