**Core Concept**
In pathology, hypertrophy refers to a reversible increase in the size of cells or organs in response to an increased workload or demand. This adaptation enables the affected cells or tissues to perform their functions more efficiently.

**Why the Correct Answer is Right**
Hypertrophy is characterized by an increase in the size of cells, which is achieved through an increase in the synthesis of cellular components, such as proteins, organelles, and other cellular structures. This process allows the cells to perform their functions more efficiently, but it does not involve an increase in the number of cells. The cellular machinery is adapted to meet the increased demand, and this adaptation is reversible. In the case of cardiac muscle cells, for example, hypertrophy occurs in response to increased workload, such as in hypertension or aortic stenosis.

**Why Each Wrong Option is Incorrect**
**Option A:** Increase no. of cells. This is actually hyperplasia, a different pathological process characterized by an increase in the number of cells.
**Option C:** Increase protein in cells. While it is true that protein synthesis increases during hypertrophy, this is not the defining characteristic of hypertrophy. The increase in protein is a consequence of the overall increase in cell size.
**Option D:** Decrease in cell number. This is actually atrophy, a pathological process characterized by a decrease in cell size and number.

**Clinical Pearl / High-Yield Fact**
It's essential to distinguish between hypertrophy and hyperplasia, as these two processes have different implications for treatment and prognosis. Hypertrophy is typically reversible, whereas hyperplasia is often a sign of a more severe underlying condition.

**✓ Correct Answer: B. Increase size of cells**