Which of the following is most suitable for the core of electromagnets?

Explain diamagnetism and diamagnetic substances.

If $\chi$ stands for the magnetic susceptibility of a substance, $\mu$ for its magnetic permeability, and $\mu_0$ for the permeability of free space, then which of the following is correct?

The resultant force acting on a diamagnetic material in a non-uniform magnetic field is in the direction . . . . . . .

Steel is preferred over soft iron for permanent magnets because

What is the Meissner effect? Explain.