The correct answer is (A) Cheerfulness; lightheartedness; elasticity or resiliency of spirit, ability to bounce back from setbacks. Also, the ability to remain afloat or to rise (to the surface).

Buoyancy comes from Old French buoyant, Spanish boyar (to float).

Examples of use:

• His buoyancy of disposition makes him a pleasure to work with.
• Salt water provides greater buoyancy than does fresh water.