Concept:Rural-urban migration involves the movement of people from rural (source) areas to urban (destination) areas, which reduces the population left behind in the source region.
Explanation:The source region is the rural area from which people move away.
As many people leave, the number of residents in that rural area decreases.
This continuous outflow of people causes a noticeable decline in the rural population.
Such a decline is described as rural depopulation.
It also leads to other effects like shortage of labour and ageing population.
Rural unemployment is not caused by people leaving; in fact, it may reduce as fewer workers remain.
Urban depopulation refers to a fall in city population, which is not the case here.
Rural congestion means overcrowding in rural areas, which is opposite to the effect of out-migration.
Answer:B. Rural depopulation