The moment of inertia of a body is a measure of its resistance to rotational motion about an axis. It depends on the mass distribution of the body and the axis of rotation.

Moment of Inertia of a Circular Plate:
The moment of inertia of a circular plate of radius R and mass M about its axis of symmetry (perpendicular to the plate) is given by the formula:

I = (1/2)MR^2

where I is the moment of inertia, M is the mass of the plate, and R is the radius of the plate.

Moment of Inertia of a Square Plate:
The moment of inertia of a square plate of side L and mass M about an axis perpendicular to the plate and passing through its center of mass is given by the formula:

I = (1/6)ML^2

where I is the moment of inertia, M is the mass of the plate, and L is the side of the square plate.

Ratio of Moment of Inertia of Circular Plate to Square Plate:
To compare the moment of inertia of a circular plate and a square plate of equal depth, we need to assume that they have the same mass. Let the mass of the plates be M and let the radius of the circular plate be R and the side of the square plate be L.

Then,

Moment of inertia of circular plate, Ic = (1/2)MR^2
Moment of inertia of square plate, Is = (1/6)ML^2

Dividing both equations, we get:

Ic/Is = (1/2)MR^2 / (1/6)ML^2
= 3R^2/L^2

Since R = L/2 (both plates have equal depth), we have:

Ic/Is = 3R^2/L^2 = 3(L/2)^2/L^2 = 3/4 < />

Therefore, the ratio of moment of inertia of a circular plate to that of a square plate of equal depth is less than 1.

Conclusion:
Hence, option A is the correct answer. The moment of inertia of a circular plate is less than that of a square plate of equal depth. This means that a circular plate is easier to rotate than a square plate of the same mass and depth.