Step 1: Recall the terminology change. The condition formerly called mental retardation has been renamed intellectual disability, also termed general learning disability.
Step 2: Define the condition. Intellectual disability is a generalized neurodevelopmental disorder characterised by significantly impaired intellectual functioning together with impaired adaptive functioning, beginning in the developmental period.
Step 3: Why the distractors are wrong. Feeble mindedness, madness, and mentally unstable are outdated, non-specific, or pejorative terms that are not the accepted modern designation.