Magnetism and Matter

A magnet is placed vertically on a paper. Then the number of neutral points obtained on the paper is:
In case of electric bell if AC power supply is used then its amplitude of the supply must be sufficiently high.
When a bar magnet is placed at 90$$^{o}$$ in a uniform magnetic field, then it is acted upon by a maximum couple. For the couple to be half the maximum value, the magnet should be inclined to the magnetic field at an angle of :

A D.M.M is in tan A position in a region where $$B_H$$  is 50$$\mu $$T. When a magnet is placed at a suitable distance the deflection obtained is 45$$^{0}$$. The resultant magnetic field at the centre of the compass is

For which of the following substances, the magnetic susceptibility is independent of temperature?