Why does it become more difficult to move a magnet towards a coil when the number of turns in the coil has been increased ? (Hint : e.m.f. induced in the coil and hance the magnetic field induced by it, becomes more when the number of turns in the coil are increased. The stronger field induced opposes the motion of the magnet towards the coil)

According to Lenz's law, the direction of induced e.m.f. (or induced current) is such that it opposes the cause which produces it. As per Faraday's laws of Electromagnetic Induction, the magnitude of induced e.m.f. is directly proportional to the number of turns in the coil.
Hence, the e.m.f. induced in the coil becomes more when the number of turns in the coil are increased. As a result, a stronger magnetic field is induced that opposes the motion of magnet towards the coil with a greater force making it more difficult to move the magnet towards the coil.