**Core Concept**
High anion gap metabolic acidosis is characterized by an increase in the anion gap due to the accumulation of acidic substances in the blood. This condition arises when there is an imbalance between the intake and excretion of acids or bases. In this scenario, the pH is normal, but there is an increase in ammonia levels, which is a key factor contributing to the development of high anion gap metabolic acidosis.

**Why the Correct Answer is Right**
Ammonia (NH3) is a volatile weak base that can accumulate in the blood, leading to an increase in the anion gap. This occurs particularly in the setting of liver disease, where the liver's ability to detoxify ammonia is impaired. As ammonia levels rise, it binds to water to form ammonium ions (NH4+), which increase the anion gap. The normal pH in this scenario is a result of the body's compensatory mechanisms, such as respiratory alkalosis, which attempt to mitigate the effects of the high anion gap metabolic acidosis.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the scenario described, as it does not address the relationship between ammonia levels and high anion gap metabolic acidosis.
* **Option B:** Lactic acidosis is a cause of high anion gap metabolic acidosis, but it is not directly related to increased ammonia levels.
* **Option C:** This option is incorrect as it does not correctly describe the relationship between ammonia levels and high anion gap metabolic acidosis.

**Clinical Pearl / High-Yield Fact**
In patients with liver disease, it is essential to monitor ammonia levels closely, as elevated levels can indicate the development of high anion gap metabolic acidosis. This is a critical consideration in the management of patients with liver disease, as it can impact treatment decisions and outcomes.

**Correct Answer:** C. Lactic acidosis