**Core Concept**
Contrecoup fractures are a type of fracture that occurs on the opposite side of the impact site in the brain, often due to the force of the impact causing the brain to move within the skull and strike the opposite side. This phenomenon is commonly observed in falls from a height, where the occipital bone is the site of impact.

**Why the Correct Answer is Right**
The commonest site of contrecoup fracture in an occipital fall is the **temporal bone**. This is because the force of the impact causes the brain to move in a contralateral direction, resulting in the temporal bone being subjected to a shearing force that can lead to a fracture. The temporal bone's proximity to the occipital bone and its relatively weak structure make it more susceptible to this type of injury.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the parietal bone, while a possible site of injury, is not the most common site of contrecoup fracture in an occipital fall.
* **Option B:** This option is incorrect because the frontal bone is not typically involved in contrecoup fractures in occipital falls.
* **Option C:** This option is incorrect because the sphenoid bone, while a possible site of injury, is not the most common site of contrecoup fracture in an occipital fall.

**Clinical Pearl / High-Yield Fact**
When evaluating patients with head injuries, it is essential to consider the possibility of contrecoup fractures, particularly in cases where the initial impact site is not immediately apparent. A thorough neurological examination and imaging studies are crucial in diagnosing these types of fractures.

**Correct Answer: C. Temporal bone**