**Core Concept**
Intellectual disability, previously referred to as mental retardation, is a condition characterized by significant limitations in intellectual functioning and adaptive behavior. Intelligence quotient (IQ) scores are used to assess intellectual functioning, and the classification of intellectual disability is based on IQ scores.

**Why the Correct Answer is Right**
IQ scores between 50-70 indicate mild intellectual disability. Individuals with mild intellectual disability may have difficulties with complex tasks, problem-solving, and learning new information, but they can still learn and adapt with support. The intellectual disability classification is based on the IQ score, with mild being the mildest form of intellectual disability.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because IQ scores between 50-70 specifically indicate mild intellectual disability, not moderate intellectual disability.
**Option B:** This option is incorrect because IQ scores between 70-85 do not indicate intellectual disability, but rather average or above-average intellectual functioning.
**Option C:** This option is incorrect because IQ scores above 85 do not indicate intellectual disability, but rather above-average intellectual functioning.

**Clinical Pearl / High-Yield Fact**
Mild intellectual disability is often characterized by difficulties with complex problem-solving and learning new information, but individuals with mild intellectual disability can still learn and adapt with support.

**Correct Answer: D. IQ between 50–70 indicates mild intellectual disability.**