**Core Concept**
The most common malignant tumor of salivary glands is a type of epithelial neoplasm that arises from the salivary gland tissue. The salivary glands are composed of serous and mucous cells, which can give rise to various types of tumors.

**Why the Correct Answer is Right**
The most common malignant tumor of salivary glands is mucoepidermoid carcinoma. It is a malignant neoplasm that arises from the salivary gland tissue and is characterized by the presence of both mucous and epidermoid cells. This tumor type is often graded on a scale of 1 to 3, with grade 1 being the most favorable and grade 3 being the most aggressive. Mucoepidermoid carcinoma can occur in any of the major salivary glands, but it most commonly arises in the parotid gland.

**Why Each Wrong Option is Incorrect**
**Option A:** Adenocarcinoma is a type of malignant tumor that arises from glandular tissue, but it is not the most common malignant tumor of the salivary glands.
**Option B:** Squamous cell carcinoma is a type of malignant tumor that arises from the squamous epithelium, but it is not typically associated with the salivary glands.
**Option C:** Acinic cell carcinoma is a rare type of malignant tumor that arises from the serous cells of the salivary glands, but it is not the most common malignant tumor.

**Clinical Pearl / High-Yield Fact**
Mucoepidermoid carcinoma can present with a range of symptoms, including a painless mass, facial paralysis, and swelling of the face. It is essential to consider this tumor type in the differential diagnosis of any mass or swelling in the parotid gland.

**Correct Answer:** C. Mucoepidermoid carcinoma