**Core Concept**
Keratinization is a process where dead cells are compacted and hardened to form a protective barrier. This process is essential for the skin's integrity, particularly in areas like the hands and feet. However, abnormal keratinization can lead to conditions like hyperkeratosis.

**Why the Correct Answer is Right**
The vitamin deficiency that may lead to keratinization is Biotin deficiency. Biotin is a B-complex vitamin that plays a crucial role in carbohydrate and fat metabolism. It is also essential for the synthesis of keratin, a protein that gives structure to skin, hair, and nails. A deficiency in biotin can lead to skin lesions, hair loss, and abnormal keratinization. The skin lesions may appear as thickening of the skin, which is a result of abnormal keratinization.

**Why Each Wrong Option is Incorrect**
**Option A:** Vitamin C deficiency is known to cause scurvy, which affects collagen synthesis, but it does not directly lead to keratinization.
**Option B:** Vitamin A deficiency can cause night blindness and skin problems, but it is not directly associated with keratinization.
**Option C:** Vitamin D deficiency can cause rickets and osteomalacia, but it does not affect keratinization.

**Clinical Pearl / High-Yield Fact**
Biotin deficiency can manifest as skin lesions, hair loss, and neurological symptoms. It's essential to remember that biotin deficiency can be caused by a variety of factors, including a restrictive diet, certain medications, and genetic disorders.

**Correct Answer:** C.