**Core Concept**
Excessive vomiting leads to metabolic alkalosis due to loss of hydrogen ions (H+) and chloride ions (Cl-) from the stomach contents. This results in an increase in blood pH and bicarbonate levels.

**Why the Correct Answer is Right**
The mechanism behind metabolic alkalosis involves the loss of acidic gastric contents, which decreases the concentration of hydrogen ions in the blood. The kidneys respond by conserving bicarbonate (HCO3-) in an attempt to maintain acid-base balance. However, this conservation of bicarbonate further exacerbates the alkalosis. Additionally, the loss of chloride ions leads to a decrease in the chloride reabsorption in the kidneys, which can cause a secondary increase in sodium reabsorption. This results in hypernatremia (elevated sodium levels) and hypochloremia (low chloride levels).

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is unrelated to the metabolic changes associated with excessive vomiting. The loss of gastric contents does not directly lead to an increase in potassium levels.

**Option B:** This option is incorrect because it is a potential cause of metabolic acidosis, not alkalosis. The loss of acidic gastric contents would actually decrease the concentration of hydrogen ions in the blood, leading to acidosis.

**Option C:** This option is incorrect because it is a potential effect of metabolic alkalosis, but not a direct consequence of excessive vomiting. The kidneys may conserve bicarbonate in an attempt to maintain acid-base balance, but this is a secondary response to the initial loss of hydrogen ions.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of metabolic alkalosis is the presence of hypochloremia, which can lead to a secondary increase in sodium levels. This can be remembered using the mnemonic "HCl -> NaCl" to recall the relationship between chloride loss and sodium gain.

**Correct Answer: A. Hypernatremia and hypochloremia.**