**Core Concept**
Renal tubular acidosis (RTA) type I, also known as distal RTA, is a disorder characterized by impaired hydrogen ion secretion in the distal nephron, leading to metabolic acidosis and hypokalemia. This condition is often caused by defects in the distal convoluted tubule or collecting duct, resulting in an inability to properly acidify the urine.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of RTA type I. In this condition, the kidneys fail to properly acidify the urine due to impaired hydrogen ion secretion in the distal nephron. As a result, the blood pH becomes acidic (metabolic acidosis), and potassium levels decrease (hypokalemia). This is because potassium is secreted in exchange for hydrogen ions in the distal nephron.

**Why Each Wrong Option is Incorrect**

**Option A:** Metabolic alkalosis
* Metabolic alkalosis is actually a feature of RTA type I, as the kidneys are unable to properly acidify the urine, leading to an accumulation of bicarbonate and an increase in blood pH.

**Option B:** Hyperkalemia
* Hyperkalemia is incorrect, as RTA type I is characterized by hypokalemia (low potassium levels) due to potassium secretion in exchange for hydrogen ions.

**Option C:** Hypophosphatemia
* Hypophosphatemia is a feature of RTA type I, as the kidneys are unable to properly reabsorb phosphate in the proximal tubule.

**Option D:** Glycosuria
* Glycosuria is not a direct feature of RTA type I, although patients may have impaired glucose tolerance or diabetes mellitus due to associated conditions such as autoimmune disorders.

**Clinical Pearl / High-Yield Fact**
A key feature of RTA type I is the presence of "paradoxical aciduria," where the urine pH remains acidic despite a high blood pH, indicating impaired hydrogen ion secretion in the distal nephron.

**Correct Answer: B. Hyperkalemia. Hyperkalemia is a feature of renal tubular acidosis type I.**