Question

a) The emf will be maximum just after the coil is flat along the magnetic field and then when it moves. In this case the change in flux is maximum.

b) If the plane of the coil is perpendicular to the magnetic field and then it rotates, the change in flux is minimum. So induced emf is minimum.At the instant when its plane is perpendicular to the magnetic field the change in flux is zero.

c) the emf will change direction twice in every cycle after it becomes zero. This means when the plane of the coil is perpendicular to the magnetic field.