This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Child psychiatry, Subject name: Psychiatry
IQ is 
Select and explain. 
A. Mental age / Chronological age x 100, B. Chronological age / Mental age x 100, C. Mental age + Chronological age x 100, D. Mental age - Chronological age x 100
A: Mental age / Chronological age x 100
Answer: A: Mental age / Chronological age x 100 
Explanation: Intellectual Disability (ID), formerly known as Mental retardation. ID is defined as a disability characterised by significant limitations in both intellectual functioning and in adaptive behaviour that emerges before the age of 18 years. Wide acceptance of this definition has led to the international consensus that an assesment of both social adaptation and intelligenc quotient (IQ)are necessary to determine the level of intellectual disability. Ref: Synopsis of Psychiatry, 11e, pg 1118