## Core Concept
Mastoiditis is an infectious condition of the mastoid part of the temporal bone, often a complication of otitis media. The condition involves inflammation of the mastoid air cells. Tenderness in mastoiditis is typically related to the anatomical location of the mastoid process.

## Why the Correct Answer is Right
The correct answer, **D. Mastoid process**, is right because the mastoid process is the portion of the temporal bone that contains the mastoid air cells. In mastoiditis, these air cells become infected and inflamed, leading to pain and tenderness over the mastoid process. This area is directly related to the site of infection.

## Why Each Wrong Option is Incorrect
- **Option A:** The occipital region is not directly related to the mastoid part of the temporal bone. While it is a part of the skull, tenderness in mastoiditis is more specifically localized.
- **Option B:** The zygomatic arch, part of the zygoma bone, does not contain mastoid air cells and is not directly involved in mastoiditis.
- **Option C:** The temporoparietal region, though close to the mastoid process, is not the specific site of tenderness in mastoiditis.

## Clinical Pearl / High-Yield Fact
A key clinical feature of mastoiditis is the presence of tenderness and swelling over the **mastoid process**. This, combined with symptoms like fever and a history of otitis media, can help in diagnosing mastoiditis. A classic clinical sign is the **Gay's sign**, which is tenderness on pressing the posterior part of the mastoid.

## Correct Answer: D. Mastoid process