<prompt> IQ 20-34 -Severe MRProfound MRModerate MRMild MR  <response>: Ans. is a i.e., Severe MR The Intelligence Quotient I.Q. is calculated according to the formula:The WHO classification of mental retardation is based on the concept of IQ and includes the following categories:CategoryIQMild50-70Moderate35-49Severe20-34Profound20A child with IQ 70 is called mentally retarded. 