**Core Concept**
Severe dehydration in a neonate requires rapid fluid replacement to restore circulating volume and prevent organ dysfunction. The World Health Organization (WHO) recommends a specific fluid replacement strategy for neonates with severe dehydration.

**Why the Correct Answer is Right**
The correct answer is based on the WHO's guidelines for treating severe dehydration in neonates. According to these guidelines, the first hour of fluid replacement should consist of a bolus of 100 mL/kg of an isotonic fluid, such as normal saline or Ringer's lactate. This rapid fluid replacement helps to restore circulating volume, improve cardiac output, and prevent organ dysfunction. The goal is to increase the neonate's blood pressure and urine output, which indicates improved renal perfusion.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not provide a sufficient volume of fluid to address severe dehydration in a neonate. A smaller volume of fluid may not be enough to restore circulating volume and prevent organ dysfunction.
**Option B:** This option is incorrect because it does not specify the type of fluid to be used. Isotonic fluids, such as normal saline or Ringer's lactate, are recommended for fluid replacement in neonates with severe dehydration.
**Option C:** This option is incorrect because it does not provide a specific volume of fluid for the first hour of replacement. A general statement about "adequate fluid replacement" is not sufficient to guide treatment.

**Clinical Pearl / High-Yield Fact**
In neonates with severe dehydration, it's essential to monitor urine output and blood pressure during fluid replacement. A urine output of at least 1 mL/kg/hour and a blood pressure above the 5th percentile for age are important indicators of adequate fluid replacement.

**Correct Answer:** A. 100 mL/kg.