**Core Concept**
Radionuclide imaging involves the use of small amounts of radioactive materials to diagnose or treat diseases. In skeletal imaging, the goal is to visualize the structure and function of bones. The most useful radio pharmaceutical for this purpose is one that selectively targets bone tissue and produces a clear image.

**Why the Correct Answer is Right**
The correct answer is Technetium-99m Methylene Diphosphonate (Tc-99m MDP). Tc-99m MDP is a radiopharmaceutical that selectively binds to hydroxyapatite in bone, making it a useful agent for skeletal imaging. It is taken up by bone cells, and its accumulation in bone tissue allows for the visualization of bone structure and function. Tc-99m MDP is widely used in nuclear medicine for imaging bone metastases, osteomyelitis, and other bone disorders.

**Why Each Wrong Option is Incorrect**
**Option A:** Technetium-99m Pyrophosphate (Tc-99m PYP) is primarily used for imaging myocardial infarction and not for skeletal imaging.
**Option B:** Gallium-67 citrate is used for imaging infections, tumors, and inflammatory conditions, but it is not the best choice for skeletal imaging.
**Option C:** Indium-111 labeled white blood cells are used for imaging infections and inflammatory conditions, but they are not specific to bone tissue.

**Clinical Pearl / High-Yield Fact**
Tc-99m MDP is a good example of a radiopharmaceutical that selectively targets bone tissue, making it a useful agent for skeletal imaging.

**Correct Answer:** C. Technetium-99m Methylene Diphosphonate (Tc-99m MDP).