$A$ hereditary disease which is never passed on from father to son is

Select the incorrect statement.

If $|a| < 1$ and $b = \sum_{k=1}^{\infty} \frac{a^k}{k}$,then $a$ is equal to

Which one of the following pairs is incorrectly matched?

Two electrons occupying the same orbital are distinguished by

$A$ long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is $B$. It is then bent into a circular loop of $n$ turns. The magnetic field at the centre of the coil will be