**Core Concept**
The question is testing the student's knowledge of the histological types of lung cancer and their metastatic potential. Lung cancer is a heterogeneous disease with various histological subtypes, each with distinct clinical and pathological characteristics. The most common histological forms of lung cancer include adenocarcinoma, squamous cell carcinoma, small cell carcinoma, and large cell carcinoma.

**Why the Correct Answer is Right**
The most common histological form of lung cancer that metastasizes is adenocarcinoma. Adenocarcinoma is a type of non-small cell lung cancer (NSCLC) that originates in the glandular cells, which are found in the terminal bronchioles and alveoli of the lung. Adenocarcinoma has a higher propensity for metastasis due to its early invasion into the airspaces and the lymphatic system. This type of cancer often spreads to distant sites, including the brain, bones, and liver, making it a highly malignant form of lung cancer.

**Why Each Wrong Option is Incorrect**
**Option A:** Squamous cell carcinoma is another common type of NSCLC, but it is less likely to metastasize compared to adenocarcinoma. Squamous cell carcinoma tends to grow locally and invades the surrounding tissues before spreading to distant sites.
**Option B:** Small cell carcinoma is a highly aggressive and malignant form of lung cancer, but it is less common than adenocarcinoma. Small cell carcinoma often presents with widespread metastasis at the time of diagnosis, but it is not the most common histological form of lung cancer that metastasizes.
**Option C:** Large cell carcinoma is a heterogeneous group of NSCLC that does not have distinct histological features. While large cell carcinoma can metastasize, it is not as common as adenocarcinoma in this regard.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the histological type of lung cancer is a critical factor in determining the prognosis and treatment plan. Adenocarcinoma is the most common type of lung cancer in non-smokers, and it often presents with early-stage disease. Therefore, early detection and treatment are crucial for improving outcomes in patients with adenocarcinoma.

**Correct Answer:** A. Adenocarcinoma