**Core Concept**
Autism Spectrum Disorder (ASD) is characterized by persistent deficits in social communication and social interaction across multiple contexts, including difficulties with verbal and nonverbal communication, and restricted, repetitive patterns of behavior, interests, or activities.

**Why the Correct Answer is Right**
Tinu's delayed speech and disinterest in social interactions with other children suggest difficulties in social communication and interaction. His fascination with spinning objects, such as fans and washing machines, is a classic example of restricted interests often seen in individuals with ASD. The parents' observation that Tinu is disinterested and self-centered further supports this diagnosis. In ASD, individuals often exhibit difficulties with social initiations and may appear to be self-centered or aloof.

**Why Each Wrong Option is Incorrect**
**Option B:** Sibling Rivalry is a common phenomenon in families with multiple children, but it does not account for Tinu's delayed speech, restricted interests, or difficulties in social interaction.

**Option C:** Mental Retardation (now known as Intellectual Disability) is characterized by significant impairments in cognitive functioning and adaptive behavior. While Tinu may have some developmental delays, there is no indication of significant cognitive impairment.

**Option D:** Specific Learning Disability refers to difficulties with academic skills such as reading, writing, or math, which are not mentioned in the scenario.

**Clinical Pearl / High-Yield Fact**
In ASD, individuals often exhibit difficulties with social initiations and may appear to be self-centered or aloof. However, they may also exhibit intense interests in specific topics or activities, which can be a clue to the diagnosis.

**✓ Correct Answer: A. Autism Spectrum Disorder**