The centre of buoyancy of a floating object is
A. at the centre of gravity of the object
B. at the centre of gravity of the submerged part of the object
C. at the centre of gravity of the remaining part outside the fluid of the object.
D. at the centre of gravity of the fluid displaced by the submerged art of the object

Hint: An object is said to float when the object has density less than the density of the water. Floatation of a body or an object depends upon its density. The principle of floatation is stated by Archimedes.

Complete answer:
The principle of floatation states that when an object or a body flows on a liquid then the buoyant force which acts on the object or the body is equal to the weight of the object.
The displaced volume of the fluid is equal to the volume of the object which is immersed in the fluid. When the weight of the object is greater than the upthrust, then the object will sink in the fluid. When the weight of the object is equal to the upthrust, then the object is balanced making the object float.
Archimedes states that all the objects which are placed in a liquid experience an upward force which allows the body to float, and it displaces water with the weight equal to the weight of the body or the object. This upward force acting on the object is known as buoyant force and the law is known as the law of buoyancy. The law of floatation is an application of Archimedes' principle.
Thus, as we know the centre of buoyancy is defined as the centre of gravity of the volume of the displaced fluid when an object is immersed in the fluid. The centre of buoyancy of a floating object is at the centre of gravity of the fluid displaced by the submerged art of the object

Hence, option (D) is the correct answer.

Note:
When any boat displaces a weight of water equal to its own weight, it floats. This phenomenon is known as the principle of flotation. It states that the floating object displaces a weight of fluid which is equal to its own weight.