$\mathrm{M}=\mathrm{I} \times \pi \mathrm{R}^{2}$
$\mathrm{B}=\frac{\mu_{0} \mathrm{I}}{2 \mathrm{R}} \Rightarrow \mathrm{I}=\frac{2 \mathrm{BR}}{\mu_{0}}$
So, $ \mathrm{M}=\frac{2 \mathrm{BR}}{\mu_{0}} \times \pi \mathrm{R}^{2}$

What is the resistance of the given galvanometer? (In $\Omega$)

Reason : The magnetic field inside the solenoid is uniform.