**Core Concept**
The question is testing the normal growth and development milestones in children, specifically the expected height at a certain age. According to the World Health Organization (WHO) growth charts, a child's height is expected to be around 100 cm at a specific age.

**Why the Correct Answer is Right**
At 4 years of age, a child's height is expected to be approximately 100 cm, which is within the normal range for this age group. This is because the average rate of growth in height is around 5-6 cm per year during the preschool age. By 4 years, a child has typically experienced three years of growth, resulting in a height of around 100 cm. This is a critical milestone in pediatric development, and healthcare providers use growth charts to monitor children's growth and identify any potential issues.

**Why Each Wrong Option is Incorrect**
**Option A:** 2 years is too early for a child to reach a height of 100 cm, as at this age, the average height is around 80-90 cm.
**Option B:** 3 years is also too early, as the average height at this age is around 90-95 cm.
**Option D:** 5 years is too late, as by this age, the average height is around 110-115 cm.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that growth charts are a crucial tool in pediatric development, and any significant deviation from the expected growth curve can indicate underlying issues, such as growth hormone deficiency, malnutrition, or chronic illness.

**✓ Correct Answer: C. 4 years**