Mental retardation is defined as IQ less than-

**Core Concept**
Mental retardation, now more appropriately referred to as intellectual disability, is a neurodevelopmental disorder characterized by significant limitations in both intellectual functioning and adaptive behavior, which covers a range of everyday social and practical skills. The diagnosis is primarily based on the level of cognitive impairment and adaptive functioning. Intelligence Quotient (IQ) scores are often used to assess intellectual functioning.

**Why the Correct Answer is Right**
The World Health Organization (WHO) and the American Association on Intellectual and Developmental Disabilities (AAIDD) define intellectual disability as an IQ score below 70, with limitations in both intellectual functioning and adaptive behavior. This cutoff score is chosen because it is significantly below the average IQ score of 100, and it is rare to find individuals with IQ scores below 70 who do not have significant limitations in adaptive behavior. The IQ score is a standardized measure of cognitive ability, and a score below 70 indicates a significant deficit in cognitive functioning.

**Why Each Wrong Option is Incorrect**
**Option A:** An IQ score below 85 might indicate a learning disability or a mild cognitive impairment, but it is not considered intellectual disability.
**Option B:** An IQ score around 100 is considered average intelligence, and it does not meet the criteria for intellectual disability.
**Option C:** An IQ score above 70, even if it is below 85, does not meet the criteria for intellectual disability.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the diagnosis of intellectual disability should not be based solely on IQ scores, but also on the individual's adaptive behavior and functional abilities. Additionally, the term "mental retardation" is considered outdated and stigmatizing, and it is now replaced by the term "intellectual disability."

**Correct Answer: C. 70**