Question

What is neutral buoyancy ?

Answer 1

Neutral buoyancy is a condition in which a physical body's average density is equal to the density of the fluid in which it is immersed.
The buoyancy offsets the force of gravity that would otherwise cause the object to sink (if the body's density is greater than the density of the fluid in which it is immersed) or rise (if it's less). An object that has neutral buoyancy will neither sink nor rise.

Example:
In scuba diving it is very important to maintain the state of neutral buoyancy. This is done by controlled breathing. The concept of life jackets originated from here.
Today this concept is applied to reduce the density of various devices so that they can float.

Applications:
This concept is useful for scuba drivers, engineers as it assists them with technology to make submarines, boats etc. It is also useful to train astronauts for the mock conditions of microgravity.

When the condition of neutral buoyancy takes place then the object seems to be in the middle that is in between the surface and the bottom.