Concept:Optimum population is the ideal population size that gives the highest possible standard of living.
Explanation:Standard of living is best measured by income per head.
At the optimum population level, the number of people is perfectly matched with the available resources, capital, and technology.
This full balance allows each worker to be productive and gainfully employed.
When population is below optimum, resources are underused and output per person is low.
When population is above optimum, resources become insufficient and per capita income falls.
Therefore, only at the optimum point does an economy attain the highest level of income per head.
Answer:B. Income per head