**Core Concept**
At 2 years of age, children are expected to have a vocabulary of around 50 words, which is a significant milestone in language development. This is a critical period in the acquisition of language skills, and children typically go through a rapid expansion of their vocabulary during this time.

**Why the Correct Answer is Right**
The correct answer reflects the average number of words a 2-year-old child is expected to know. This is based on the typical language development timeline, where children start with a vocabulary of around 10-20 words at 18 months and rapidly expand to around 50 words by 2 years of age. This vocabulary growth is essential for communication and lays the foundation for future language skills.

**Why Each Wrong Option is Incorrect**
**Option A:** 5 words - This is too low, as most 2-year-olds have a vocabulary of at least 20-30 words by this age.
**Option B:** 100 words - This is too high, as while some 2-year-olds may have a more advanced vocabulary, 100 words is typically not the average for this age group.
**Option C:** 200 words - This is also too high, as most 2-year-olds are still learning to communicate effectively and have not yet developed a vocabulary of this size.

**Clinical Pearl / High-Yield Fact**
Remember that language development can vary significantly among children, and some may have a more advanced or delayed vocabulary. It's essential to consider the child's overall development, including cognitive, social, and emotional skills, when evaluating language development.

**Correct Answer:** C. 50 words