**Core Concept**
Hemochromatosis is a genetic disorder characterized by excessive iron absorption, leading to iron overload and subsequent tissue damage. This condition affects multiple organ systems, including the skin, joints, and endocrine glands.

**Why the Correct Answer is Right**
The patient's symptoms of arthritis, hyperpigmentation of the skin, and hypogonadism are classic manifestations of hemochromatosis. Iron overload in this condition leads to the deposition of iron in the skin, causing hyperpigmentation. Similarly, iron deposition in the joints leads to arthritis, while the accumulation of iron in the endocrine glands, particularly the pituitary gland, results in hypogonadism. The genetic mutation responsible for hemochromatosis affects the HFE gene, which is involved in regulating iron absorption.

**Why Each Wrong Option is Incorrect**
**Option B:** Ectopic ACTH secreting tumor of the lung typically presents with Cushing's syndrome, characterized by weight gain, hypertension, and hyperglycemia, rather than the combination of arthritis, hyperpigmentation, and hypogonadism seen in hemochromatosis.
**Option C:** Wilson's disease is a genetic disorder that leads to copper accumulation in the body, primarily affecting the liver and brain. While it can cause liver disease and neurological symptoms, it does not typically present with the combination of arthritis, hyperpigmentation, and hypogonadism seen in hemochromatosis.
**Option D:** Rheumatoid arthritis is a chronic autoimmune disorder that affects the joints, but it does not typically cause hyperpigmentation of the skin or hypogonadism.

**Clinical Pearl / High-Yield Fact**
Hemochromatosis should be suspected in patients with a family history of the condition, particularly those of Northern European descent, and those who present with a combination of arthritis, hyperpigmentation, and endocrine dysfunction.

**✓ Correct Answer: A. Hemochromatosis**