Choice A rationale:

Fluid deficit (in mL) = body weight (in kg) x 0.03.

Rationale: This calculation significantly underestimates the fluid deficit for a child with moderate dehydration.

Dehydration often requires more significant fluid replacement.

Choice B rationale:

Fluid deficit (in mL) = body weight (in kg) x 0.06.

Rationale: This calculation overestimates the fluid deficit for a child with moderate dehydration.

Using this formula would result in excessive fluid replacement, which can be harmful.

Choice C rationale:

Fluid deficit (in mL) = body weight (in kg) x 0.1.

Rationale: This calculation overestimates the fluid deficit for a child with moderate dehydration.

Using this formula would result in excessive fluid replacement, which can be harmful.

Choice D rationale:

Fluid deficit (in mL) = body weight (in kg) x 0.04.

Rationale: This is The correct answer.

The appropriate fluid deficit calculation for a child who weighs 12 kg with moderate dehydration is to multiply their body weight by 0.04.

For this child, it would be 12 kg x 0.04 = 480 mL.

This formula is a commonly used guideline to estimate fluid deficit in cases of dehydration.