<prompt> Mental retardation is defined if IQ is below -90807060  <response>: Ans. is c i.e., 70 A child with IQ 70 is called mentally retarded. The WHO classification of mental retardation is based on the concept of IQ and includes the following categories:CategoryIQMild50-70Moderate35-49Severe20-34Profound20 A child with IQ 70 is called mentally retarded. 