**Core Concept**
Acute diarrhea in children often leads to a state of dehydration, characterized by decreased serum sodium (hyponatremia) and chloride levels, along with metabolic acidosis. The primary goal of fluid therapy is to correct the fluid deficit, maintain electrolyte balance, and restore acid-base balance.

**Why the Correct Answer is Right**
In this scenario, the child presents with hyponatremia (Na+ 125 mEq/L) and metabolic acidosis (HCO3- 16 mEq/L, pH 7.23). Normal saline (0.9% NaCl) is the preferred initial fluid choice because it contains an isotonic concentration of sodium and chloride ions, which helps to correct the fluid deficit, increase sodium levels, and improve acid-base balance. The addition of potassium supplements may be necessary to correct hypokalemia (K+ 3 meq/L).

**Why Each Wrong Option is Incorrect**
**Option B:** 3% saline is hypertonic and would worsen hyponatremia if administered in large quantities. It is typically used in the treatment of severe hyponatremia with symptoms of cerebral edema.
**Option C:** N/2 saline + 10% dextrose is a hypotonic solution that may worsen hyponatremia and is not suitable for initial fluid resuscitation in this scenario. Dextrose is added to provide calories, but it does not correct electrolyte imbalances.
**Option D:** N/3 saline + 5% dextrose is also a hypotonic solution that may exacerbate hyponatremia. The addition of dextrose provides calories, but it does not address the underlying electrolyte imbalances.

**Clinical Pearl / High-Yield Fact**
In pediatric patients with acute diarrhea, the initial fluid resuscitation should aim to correct the fluid deficit and maintain electrolyte balance. Normal saline is the preferred initial fluid choice, and potassium supplements may be necessary to correct hypokalemia. In severe cases, consider consulting a pediatrician or a critical care specialist for further management.

✓ Correct Answer: A. Normal saline