**Core Concept**
The periodontal probe is a dental instrument used to measure the depth of the periodontal pockets in the gums. It comes in various types, each with distinct features that aid in precise measurements and assessments.

**Why the Correct Answer is Right**
The probe with a ball at its tip is known as a "ball probe." This design allows for smooth penetration into the periodontal pocket and prevents the probe from getting wedged or stuck, which can cause discomfort to the patient. The ball-shaped tip also minimizes the risk of causing damage to the surrounding tissues. The ball probe is particularly useful for measuring the depth of deep periodontal pockets.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it is not specified which type of probe is being described. Without further details, it is impossible to determine if this probe has a ball at its tip.
* **Option B:** This option is incorrect because it may describe a different type of dental instrument, such as a periodontal explorer, which is used for detecting calculus and other abnormalities, but does not have a ball-shaped tip.
* **Option C:** This option is incorrect because it may describe a different type of periodontal probe, such as a UNC probe, which has a straight or tapered tip, but not a ball-shaped tip.

**Clinical Pearl / High-Yield Fact**
When using periodontal probes, it is essential to choose the correct type based on the specific needs of the patient and the clinical scenario. A ball probe is particularly useful for deep periodontal pockets, while a UNC probe is better suited for shallow pockets.

**Correct Answer:** C.