**Core Concept:** Differential diagnosis is a process of eliminating or confirming the most likely diagnosis based on a thorough clinical examination, history, and investigations. In congenital disorders of pigmentation, we need to consider various types of pigmentary disorders.

**Why the Correct Answer is Right:** The correct answer, **C. Vitiligo**, is a common acquired autoimmune disorder that results in hypopigmentation due to selective destruction of melanocytes. The immune system attacks melanocytes, leading to the loss of pigment and development of white patches on the skin.

**Why Each Wrong Option is Incorrect:**

A. **Hypopigmentation:** This option is incorrect because it is a general term for reduced melanin production in the skin or hair. It does not specify any particular disorder.

B. **Hyperpigmentation:** This option is incorrect because it refers to increased melanin production, which is opposite to the condition described in the correct answer.

D. **Pigmentation disorders:** This option is incorrect because it is too broad and does not specify the correct diagnosis, Vitiligo.

**Clinical Pearl / High-Yield Fact:** Vitiligo has an autoimmune basis, and its management involves repigmentation therapy, photoprotection, and management of complications such as skin cancer.

**Correct Answer:** C. Vitiligo

**Explanation:** Vitiligo is a common autoimmune disorder resulting in hypopigmentation due to the destruction of melanocytes. It is characterized by the presence of white patches on the skin, hair, and mucous membranes. The cause of vitiligo is an autoimmune response against melanocytes, leading to melanin depletion and hypopigmentation. The differential diagnosis of congenital disorders of pigmentation should consider various types of pigmentary disorders, including acquired disorders like vitiligo and inherited disorders like Albright's hereditary osteodystrophy and Waardenburg syndrome.