Correct option is (a) Ib=\(\int _0 ^R\)mr^2dr
For explanation: Moment of inertia or rotational inertia of the rotor blade about the center of rotation is given by:
Ib=\(\int _0 ^R\)mr^2dr
Where, m is the blade’s mass per unit length which is a function of r
r is radial location of the blade measured from center (r=0) to the tip (r=R)