Hey mate,
Q6: Key thing is that the Oval is not centred around the magnetic pole, keeping in mind that the magnetic field would be weaker the further away from the pole that it is (just like further away from a bar magnet -- B-field gets weaker), so the answer is A. What you say about magnetic field strength being independent of area is only true if the magnetic field is of constant strength, whereas in this scenario, B-field is not constant.
Q7: This is referring to how AC can be stepped up/down and hence different instruments requiring different voltages can all run off the same AC source, hence more easily adapted
Q8: Speed of an AC motor is limited by the rate at which the AC input signal changes (i.e., frequency), not the magntiude of current/voltage itself. So, regardless of voltage, the maximum speed of an AC motor connected to our typical AC supply would be 50Hz or 3000rpm.