Concept:Residual unemployment refers to unemployment caused by personal disabilities that prevent a person from working.
Explanation:Unemployment can arise from different causes, such as lack of skills, economic downturns, or job changes.
When unemployment occurs specifically because a worker has a physical or mental disability, the person is often unable to participate in normal employment at all.
Such workers remain outside the labour force even during periods of full employment.
Economists call this category residual unemployment because it persists despite general economic conditions.
Frictional, structural, and cyclical unemployment do not arise from disability.
Therefore, the type described in the question is residual unemployment.
Answer:D. residual unemployment