**Core Concept**
The hydrostatic test, also known as the "float test," is used to determine if a fetus was born alive or stillborn. This test is based on the principle that the lungs of a stillborn fetus will not contain air and will therefore sink in water, whereas the lungs of a live-born fetus will contain air and will float.

**Why the Correct Answer is Right**
A false negative hydrostatic test in a live-born fetus occurs when the lungs appear to sink in water, suggesting the fetus was stillborn, but this result is incorrect. This can happen due to various factors such as atelectasis (collapsed lung tissue), which prevents the lungs from floating.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not relate to the specific scenario of a false negative hydrostatic test.
**Option B:** This option is also incorrect as it does not provide a valid reason for a false negative result.
**Option C:** Similarly, this option does not offer a plausible explanation for the false negative test result.
**Option D:** This option is incorrect because it is not relevant to the context of the hydrostatic test.

**Clinical Pearl / High-Yield Fact**
It's crucial to remember that the hydrostatic test is not foolproof and can yield false negative results, especially if the live-born fetus had significant respiratory distress or other lung conditions.

**Correct Answer:** D. atelectasis of lungs