## Core Concept
The classification of mental retardation, now more appropriately referred to as intellectual disability, is based on the intelligence quotient (IQ) and adaptive behaviors. Intellectual disability is characterized by significant limitations in both intellectual functioning and adaptive behavior, which covers a range of everyday social and practical skills. The IQ is a key measure used to assess intellectual functioning.

## Why the Correct Answer is Right
The classification of intellectual disability is as follows: mild intellectual disability (IQ levels 50-69), moderate intellectual disability (IQ levels 35-49), severe intellectual disability (IQ levels 20-34), and profound intellectual disability (IQ levels below 20). Therefore, a child with profound mental retardation, or intellectual disability, would have an IQ below 20. This level of intellectual disability indicates significant limitations in intellectual functioning and adaptive behaviors, requiring substantial support.

## Why Each Wrong Option is Incorrect
* **Option A:** While an IQ of 20-34 indicates severe intellectual disability, it does not meet the criteria for profound intellectual disability.
* **Option B:** An IQ of 35-49 corresponds to moderate intellectual disability, which is also not indicative of profound intellectual disability.
* **Option C:** This option is not provided, but based on the context, any IQ range above 20 would not classify as profound intellectual disability.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the classification of intellectual disability into mild, moderate, severe, and profound categories helps guide the level of support required for an individual. Profound intellectual disability (IQ < 20) requires the most substantial support, often including full-time caregivers for daily living activities. ## Correct Answer: D. Below 20.