**Core Concept**
Intellectual disability, also known as mental retardation, is a condition characterized by significant cognitive and adaptive functioning impairments. The Intelligence Quotient (IQ) score is used to assess cognitive abilities, with a normal IQ range typically considered to be between 85 and 115.

**Why the Correct Answer is Right**
The given chronological age of 10 years and mental age of 4 years indicate a significant discrepancy in cognitive development. This is calculated using the Intelligence Quotient (IQ) formula: IQ = (Mental Age / Chronological Age) x 100. In this case, the IQ is (4 / 10) x 100 = 40. An IQ score of less than 70 is generally considered to be indicative of intellectual disability. The individual in question would be classified as having a mild intellectual disability, which is characterized by an IQ score between 50 and 70.

**Why Each Wrong Option is Incorrect**
* **Option A:** There is no information provided to support the classification of this individual as having a severe intellectual disability, which is characterized by an IQ score below 40.
* **Option B:** The term "mild mental retardation" is an outdated term and has been replaced by "mild intellectual disability."
* **Option C:** The term "profound mental retardation" is also an outdated term and has been replaced by "profound intellectual disability," which is characterized by an IQ score below 20.

**Clinical Pearl / High-Yield Fact**
The IQ score is a useful tool for assessing cognitive abilities, but it should be interpreted in the context of the individual's adaptive functioning and overall development.

**Correct Answer:** D.