## **Core Concept**
The Intelligence Quotient (IQ) is a measure used to assess human intelligence. It is calculated by dividing the mental age by the chronological age and then multiplying by 100. This can be expressed as: **IQ = (Mental Age / Chronological Age) * 100**.

## **Why the Correct Answer is Right**
Given that the child has a mental age of 2 years and a chronological age of 10 years, we can substitute these values into the IQ formula: **IQ = (2 / 10) * 100 = 20**. This calculation directly leads to the correct answer.

## **Why Each Wrong Option is Incorrect**
- **Option A:** 10 - This would imply that the mental age equals the chronological age (IQ = 10 / 10 * 100 = 100), which is not the case here.
- **Option B:** 5 - This would imply an IQ calculation of (5 / 10) * 100 = 50, which does not match our calculation.
- **Option D:** 25 - This would imply an IQ calculation of (2.5 / 10) * 100 = 25, which also does not match.

## **Clinical Pearl / High-Yield Fact**
A significant clinical pearl is that an IQ score of 20 falls into the category of profound intellectual disability. This scoring system helps in categorizing the level of intellectual disability and planning appropriate interventions.

## **Correct Answer:** . 20