Social & Preventive Medicine Mental Health 29302b53 Mental retardation is defined if IQ is below:- A 60 B 70 C 80 D 90 High-Yield Explanation Normal IQ 70 or above. Mild mental retardation = 50-70 Moderate mental retardation = 35-49 Severe mental retardation = 20-34 Profound mental retardation = <20.