**Core Concept**
The Lund and Browder chart is a widely used method for estimating the percentage of body surface area (BSA) affected by burns in children. This chart takes into account the varying proportions of body surface area in different age groups, including infants and children.

**Why the Correct Answer is Right**
To calculate the percentage of burns on the head, neck, and face in a child of one year, we use the Lund and Browder chart. The head, neck, and face make up approximately 18% of the total body surface area in a one-year-old child. This percentage is based on the proportion of surface area covered by these regions in a standard child's body, which is larger compared to adults.

**Why Each Wrong Option is Incorrect**
* **Option A:** The percentage of burns on the head, neck, and face in a one-year-old child is not 4% (Option A). This value is too low and does not account for the larger surface area of the head, neck, and face in infants.
* **Option B:** The percentage of burns on the head, neck, and face in a one-year-old child is not 20% (Option B). This value is too high and exceeds the actual proportion of surface area covered by these regions in a standard child's body.
* **Option C:** The percentage of burns on the head, neck, and face in a one-year-old child is not 12% (Option C). This value is too low and does not accurately reflect the larger surface area of the head, neck, and face in infants.

**Clinical Pearl / High-Yield Fact**
When assessing burns in children, it is essential to use the Lund and Browder chart to accurately estimate the percentage of body surface area affected. This allows for proper wound management and prevents underestimation or overestimation of burn severity.

**Correct Answer:** **A. 18%**