Thank you for reporting, we will resolve it shortly
Q.
The ratio of magnetic field at the centre of a current carrying circular coil to its magnetic moment is ‘x’ if the current and the radius both are doubled. The new ratio will become
Magnetic field at the center of the current carrying loop is given by
$B =$ $\left(\mu_{0} / 4 \pi\right) \times(2 \pi i / a )=\left(\mu_{0} i \right) / 2 a .$
Magnetic moment at the center of the current carrying loop is given by
$M=\pi a ^{2}$
thus $B / M =\mu_{0} /\left(2 \pi a ^{3}\right)= x ($ given $)$
when both current and radius are doubled ratio become $x / 8$ times.