**Core Concept**
Specific learning disability refers to a neurodevelopmental disorder characterized by difficulties in learning and using specific academic skills, such as reading, writing, or mathematics, despite average to above-average intelligence and adequate instruction. This condition is not caused by low intelligence, lack of motivation, or poor teaching, but rather by underlying differences in brain function and processing.

**Why the Correct Answer is Right**
The boy's symptoms, including difficulty in expressing himself in writing, frequent spelling mistakes, and inability to follow instructions, are indicative of a specific learning disability, particularly dysgraphia or dyslexia. These conditions affect the brain's ability to process and integrate information, leading to difficulties in learning and using specific academic skills. The boy's inability to wait for his turn while playing a game may also suggest difficulties with executive function, a common feature of specific learning disabilities.

* **Option A:** Mental retardation is a condition characterized by significantly below-average intelligence, which is not indicated in this case.
* **Option B:** Lack of interest in studies may be a contributing factor, but it does not fully explain the boy's specific difficulties in academic skills.
* **Option D:** Examination anxiety can cause temporary difficulties, but it does not account for the boy's persistent and specific learning difficulties.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that specific learning disabilities are not the result of poor teaching, lack of motivation, or low intelligence. Instead, they are neurodevelopmental disorders that require targeted interventions and accommodations to help individuals with these conditions succeed academically and professionally.

**✓ Correct Answer: C. Specific learning disability**