**Core Concept**
The normal platelet count, also known as thrombocytosis, is a physiological condition where the platelet count in the peripheral blood is within the normal range. This is distinct from thrombocytopenia, which is a condition characterized by an abnormally low platelet count. Platelets play a crucial role in blood clotting and are essential for maintaining hemostasis.

**Why the Correct Answer is Right**
The correct answer is based on the definition of a normal platelet count, which is generally considered to be between 150,000 to 450,000 platelets per microliter (μL) of blood. This range may vary slightly depending on the laboratory and the method used to measure platelet count. The normal platelet count is a reflection of the body's ability to produce and regulate platelets effectively. The bone marrow is responsible for producing platelets, and the spleen plays a role in filtering and storing platelets.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a normal platelet count. A platelet count of 100,000/μL is below the normal range and would be considered thrombocytopenic.
**Option B:** This option is incorrect because it does not provide a specific platelet count. A range of 100,000 to 200,000/μL is below the normal range and would be considered thrombocytopenic.
**Option C:** This option is incorrect because it does not provide a specific platelet count. A range of 500,000 to 600,000/μL is above the normal range and would be considered thrombocytosis.

**Clinical Pearl / High-Yield Fact**
A normal platelet count is essential for maintaining hemostasis and preventing bleeding disorders. Thrombocytopenia can increase the risk of bleeding, while thrombocytosis can increase the risk of clotting.

**Correct Answer:** D.