**Core Concept**
Social smile is a milestone in infant development that signifies a shift from reflexive smiling to intentional and social smiling. It is characterized by a smile in response to social interaction, such as being spoken to or seeing a familiar face.

**Why the Correct Answer is Right**
The development of a social smile is a significant cognitive and social milestone in infancy, typically occurring between 8-12 weeks of age. This is a time when infants begin to understand the connection between their actions and the reactions of others, and they start to exhibit more intentional and social behavior. The development of a social smile is closely linked to the maturation of the brain's social cognition centers, including the inferior frontal gyrus and the superior temporal sulcus.

**Why Each Wrong Option is Incorrect**
**Option A:** 2 weeks - This is too early for social smile to develop, as infants at this age are still in the reflexive smiling phase.
**Option B:** 16 weeks - While some infants may start to exhibit social smiling around this age, it is generally considered to be on the later end of the typical range.
**Option C:** 6 weeks - While some infants may start to show signs of social smiling around this age, it is generally considered to be a bit early for a full social smile to be established.

**Clinical Pearl / High-Yield Fact**
The development of a social smile is a key indicator of normal cognitive and social development in infants. It is essential for pediatricians and caregivers to monitor for this milestone and to be aware of any potential delays or abnormalities.

**Correct Answer: C. 8-12 weeks.**