**Core Concept**
Children grow at varying rates, but most pediatricians use growth charts to track a child's height and weight against standardized percentiles. The height of a child typically follows a predictable pattern, with significant growth spurts during specific age ranges.

**Why the Correct Answer is Right**
At around 4.5 years of age, children often exhibit a significant growth spurt, during which they may acquire a height of approximately 100 cm. This growth is largely driven by the rapid increase in the rate of bone growth and development, particularly in the long bones of the body. The growth plates, which are areas of cartilage in the bones, allow for the continuous elongation of bones as the child grows.

**Why Each Wrong Option is Incorrect**
**Option A:** 2.5 years is too early for a child to reach a height of 100 cm, as most children at this age are still in the lower percentile ranges and have not yet experienced their first significant growth spurt.
**Option B:** 3.5 years is also too early, as children typically take another 1-2 years to reach the 100 cm mark, with the majority of growth occurring between 4-6 years of age.
**Option D:** 5.5 years is too late, as most children have already surpassed the 100 cm mark by this age.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that growth charts are not a substitute for clinical evaluation, and pediatricians must consider other factors such as parental height, family history, and overall health when assessing a child's growth and development.

**✓ Correct Answer: C. 4.5 year**