**Core Concept**
The question is testing the concept of Intelligence Quotient (IQ) and its calculation, specifically the formula for determining mental age and IQ in children. The formula is: IQ = (Mental Age / Chronological Age) x 100.

**Why the Correct Answer is Right**
To calculate the IQ of the child, we need to use the given mental age and chronological age in the formula. The child's mental age is 2 years, and chronological age is 10 years. Plugging these values into the formula: IQ = (2 / 10) x 100 = 20. This means that the child's IQ is 20.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided, so we cannot assess its correctness. However, we can proceed with the other options.
**Option B:** This option is incorrect because it does not provide a valid IQ score. IQ scores are typically calculated using the formula mentioned earlier.
**Option C:** This option is incorrect because it is a placeholder and does not represent a valid IQ score.
**Option D:** This option is incorrect because it is a placeholder and does not represent a valid IQ score.

**Clinical Pearl / High-Yield Fact**
It is essential to understand that IQ scores are not a definitive measure of intelligence and should be interpreted with caution. They can be influenced by various factors such as education, socio-economic status, and cultural background.

**Correct Answer: A. 20.**