<prompt> IQ in profound mental retardation -50 - 7035 - 5020 - 3520  <response>: Ans. is d i.e., 20 The Intelligence Quotient I.Q. is calculated according to the formula:IQ Mental age---Chronological agex 100The 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. 