The correct answer is: B. above the center of buoyancy.
The metacenter is a point on a floating body that determines whether the body will be stable or unstable. If the metacenter is above the center of buoyancy, the body will be stable. If the metacenter is below the center of buoyancy, the body will be unstable.
The center of buoyancy is the point where the upward force of buoyancy acts on a floating body. The center of gravity is the point where the weight of a body acts.
If the metacenter is above the center of buoyancy, then when the body is disturbed, the upward force of buoyancy will act to restore the body to its original position. This is because the upward force of buoyancy will act through the metacenter, which is above the center of gravity. The upward force of buoyancy will therefore create a torque that will rotate the body back to its original position.
If the metacenter is below the center of buoyancy, then when the body is disturbed, the upward force of buoyancy will act to further disturb the body. This is because the upward force of buoyancy will act through the metacenter, which is below the center of gravity. The upward force of buoyancy will therefore create a torque that will rotate the body further away from its original position.
In conclusion, for a floating body to be in stable equilibrium, its metacenter should be above the center of buoyancy.