अनुकूलतम जनसंख्या सिद्धांत (Optimum Population Theory) के अनुसार, अनुकूलतम जनसंख्या वह स्तर है जो क्या प्रदान करता है?

Given below are two statements, one labelled as Assertion (A) and the other labelled as Reason (R): Assertion (A): Migration has a direct bearing on the age composition of a population. Reason (R): Migration tends to be age-selective, meaning people in the age group of 15-30 years are more mobile than younger and older age groups. In the context of the statements above, which of the following is correct?

Which of the following groups of countries is correctly sequenced in the ascending order of their total population as per the 2016 United Nations estimates?