**Core Concept**
Proximal renal tubular acidosis (RTA) is a type of kidney disorder characterized by impaired acid secretion in the proximal convoluted tubule (PCT) of the nephron, leading to metabolic acidosis.

**Why the Correct Answer is Right**
In proximal RTA, the PCT fails to reabsorb bicarbonate (HCO3-) ions, resulting in a loss of bicarbonate in the urine. This leads to a decrease in serum bicarbonate levels, causing metabolic acidosis. The kidneys also fail to reabsorb potassium ions, leading to hypokalemia. Additionally, the condition is often associated with low levels of phosphate (hypophosphatemia) due to impaired reabsorption.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because proximal RTA is characterized by hypokalemia, not hyperkalemia. Hyperkalemia is typically seen in distal RTA, where the kidneys fail to secrete potassium ions.

**Option B:** This option is incorrect because proximal RTA is associated with hypophosphatemia, not hyperphosphatemia. The kidneys fail to reabsorb phosphate ions in this condition, leading to low serum phosphate levels.

**Option C:** This option is incorrect because proximal RTA is characterized by metabolic acidosis, not metabolic alkalosis. The kidneys fail to reabsorb bicarbonate ions, leading to a decrease in serum bicarbonate levels and acidosis.

**Clinical Pearl / High-Yield Fact**
Proximal RTA is often associated with Fanconi syndrome, a disorder characterized by impaired reabsorption of glucose, amino acids, and phosphate ions in the PCT.

**Correct Answer:** A. Hyperkalemia