Mental retardation is defined if IQ is below –

**Core Concept**
Mental retardation, now more appropriately termed intellectual disability, is a neurodevelopmental disorder characterized by significant limitations in intellectual functioning and adaptive behaviors. This condition is often associated with cognitive impairments, learning disabilities, and difficulties in social and adaptive skills.

**Why the Correct Answer is Right**
The definition of intellectual disability is based on the Intelligence Quotient (IQ) score, which is a standardized measure of cognitive ability. An IQ score below 70, as per the World Health Organization (WHO) and American Association on Intellectual and Developmental Disabilities (AAIDD), indicates intellectual disability. This threshold is used to distinguish individuals with intellectual disability from those with average or above-average intelligence.

**Why Each Wrong Option is Incorrect**
**Option A:**
This option is incorrect because an IQ score below 50 is typically associated with severe intellectual disability, whereas the correct threshold for intellectual disability is below 70.

**Option B:**
This option is incorrect because an IQ score of 85-114 is within the average range of intelligence, not indicative of intellectual disability.

**Option C:**
This option is incorrect because an IQ score above 70 does not meet the criteria for intellectual disability.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that intellectual disability is a heterogeneous condition, and IQ scores can vary widely among individuals with the same diagnosis. Additionally, IQ scores alone do not determine an individual's potential or capabilities.

**Correct Answer: D. 70**