The correct answer is: C. Weight of the body is assumed to be concentrated.
The center of gravity of a homogeneous body is the point at which the whole weight of the body is assumed to be concentrated. It is the point through which the resultant gravitational force acts on the body.
The center of gravity of a body can be found by balancing the body on a knife edge. The point at which the body balances is the center of gravity.
The center of gravity of a body can also be found by calculating the moments of inertia of the body about two axes. The axis through the center of gravity will have the smallest moment of inertia.
The center of gravity of a body is important in many applications, such as in the design of machines and structures. It is also important in sports, such as gymnastics and diving.
A. Volume of the body is assumed to be concentrated
This is not correct. The center of gravity of a body is not the point at which the whole volume of the body is assumed to be concentrated. The center of gravity is the point at which the whole weight of the body is assumed to be concentrated.
B. Area of the surface of the body is assumed to be concentrated
This is also not correct. The center of gravity of a body is not the point at which the whole area of the surface of the body is assumed to be concentrated. The center of gravity is the point at which the whole weight of the body is assumed to be concentrated.