**Core Concept**
The daily maintenance fluid for a child is calculated based on their weight to ensure adequate hydration and electrolyte balance. The World Health Organization recommends the following formula for children: 100 mL/kg/day for the first 10 kg of body weight, plus 50 mL/kg/day for the next 10 kg (up to 20 kg), and 20 mL/kg/day for each kilogram above 20 kg.

**Why the Correct Answer is Right**
For a child weighing 10 kg, the daily maintenance fluid is calculated as 100 mL/kg/day for the first 10 kg, which equals 1000 mL/day. This is because the child's weight falls entirely within the first 10 kg category, and there is no need to calculate additional fluid requirements for the next 10 kg or beyond. The correct calculation is based on the child's weight and the established formula, ensuring adequate hydration and electrolyte balance.

**Why Each Wrong Option is Incorrect**
**Option B:** This option is incorrect because it underestimates the daily maintenance fluid requirement for a 10 kg child. The formula is not met when using this amount, leading to potential dehydration and electrolyte imbalances.
**Option C:** This option is incorrect because it significantly underestimates the daily maintenance fluid requirement for a 10 kg child. The child's weight falls within the first 10 kg category, and using this amount would lead to inadequate hydration and electrolyte balance.
**Option D:** This option is incorrect because it overestimates the daily maintenance fluid requirement for a 10 kg child. While it is close to the correct answer, it exceeds the calculated amount, potentially leading to fluid overload and other complications.

**Clinical Pearl / High-Yield Fact**
When calculating daily maintenance fluids for children, remember to use the World Health Organization's formula and consider the child's weight in kilograms. This will help ensure accurate and safe fluid management, avoiding potential complications such as dehydration or fluid overload.

**✓ Correct Answer: A. 1000 ml/day**