A person could float most easily in water that has which characteristic?

It is called buoyancy.

Explanation:

When an object is immersed partly or wholly in a liquid, it experiences an upward force called buoyant force.

The buoyant force depends on the volume of body immersed, density of liquid and the acceleration due to gravity.

The force of buoyant force is given by

F = Volume of body immersed x density of liquid x g