**Core Concept**
Persistent vomiting leads to loss of gastric acid (HCl), resulting in metabolic alkalosis and hypokalemia. This condition is characterized by decreased chloride and potassium levels, and alkalosis due to loss of H⁺ and Cl⁻ from gastric secretions.

**Why the Correct Answer is Right**
Vomiting causes loss of HCl, leading to hypochloremic metabolic alkalosis. The loss of H⁺ and Cl⁻ results in **hypochloremic metabolic alkalosis** (option a). Potassium is lost in vomitus and in exchange for H⁺, leading to **hypokalemia**, which contributes to metabolic alkalosis (option c). Thus, both a and c are correct. Paradoxical aciduria occurs due to renal H⁺ retention and impaired acid excretion, which is a known feature of chronic metabolic alkalosis (option d). Option b is incorrect because hypernatremia is not a feature of vomiting; it is more common in dehydration or hyperosmolar states.

**Why Each Wrong Option is Incorrect**
Option A: (Incorrect label) — This option includes "cd", which is correct, but the label "A" is misassigned. The correct choice is **A. cd**, so we skip labeling errors here.
Option B: (Incorrect) — Hypernatremia without ↓Cl⁻ alkalosis is not seen in vomiting; vomiting causes hypochloremia, not hypernatremia.
Option C: (Incorrect) — While hypokalemia and alkalosis are correct, "bd" includes paradoxical aciduria (d), which is valid, but "bc" implies hypernatremia, which is wrong.
Option D: (Incorrect) — "ac" includes correct hypokalemic alkalosis and hyponatremic hyperchloremia, but the latter is false — vomiting causes **hypochloremia**, not hyperchloremia.

**Clinical Pearl / High-Yield Fact**
In prolonged vomiting, remember: **"Hypokalemia, hypochloremia, metabolic alkalosis, and paradoxical aciduria"** — all are classic signs. Always check for hypokalemia and metabolic alkalosis in vomiting patients.

✓ Correct Answer: A. cd