**Core Concept**
Zinc is a vital trace element involved in immune function, cell division, and protein synthesis. Deficiency impairs wound healing, reproductive function, and growth, but it does not typically cause pigmentation changes.

**Why the Correct Answer is Right**
Zinc deficiency is well-documented to cause delayed wound healing (due to impaired collagen synthesis and immune function), loss of libido, and sexual infantilism (such as reduced pubertal development and gynecomastia). However, pigmentation (e.g., hyperpigmentation or hypopigmentation) is not a classic or consistent feature of zinc deficiency. The body does not show marked skin pigmentation changes in zinc-deficient states, unlike conditions such as iron deficiency or chronic infections.

**Why Each Wrong Option is Incorrect**
Option A: Delayed wound healing is a hallmark of zinc deficiency due to impaired keratinization and immune responses.
Option B: Loss of libido occurs due to zinc’s role in testosterone production and reproductive hormone regulation.
Option D: Sexual infantilism (e.g., failure to achieve adult male characteristics) is a recognized sign of severe zinc deficiency in adolescents and adults.

**Clinical Pearl / High-Yield Fact**
Zinc deficiency primarily affects growth, immunity, and sexual maturation—never pigmentation. Always remember: **"Zinc deficiency = poor wound healing, low libido, infantilism — not pigmentation."**

✓ Correct Answer: C. Pigmentation