$\mathrm{R}=\frac{\mathrm{V}}{\mathrm{I}_{8}}-\mathrm{G}$

$\mathrm{I}_{\mathrm{R}}$ is the current in the galvenometer for full scale deflection.

For the choice $( 1)$

${\rm{R}} = \frac{{50}}{{50 \times {{10}^{ - 6}}}} - 100 \ne 10{\rm{k}}\Omega $

For the choice $(2)$

$\mathrm{R}=\frac{10}{50 \times 10^{-6}} -100=2 \times 10^{5}-100 $

$ \simeq 2 \times {10^5}\Omega $

$ \simeq 200{\rm{k}}\Omega $

Hence, the choice $( 2)$ is conrect.

Further, the galvanometer may be converted inte an ammeter if a small resistance $'s'$ is connectec (or shunted) in parallel with the galvenometer.

where $S = \frac{{{I_g}}}{{I - {I_g}}} \times G$

$I$ is the range of the annmeter.

For the choice $( 3)$

$S = \frac{{50 \times {{10}^{ - 6}}}}{{5 \times {{10}^{ - 3}} - 50 \times {{10}^{ - 6}}}} \times 100$

$ \simeq \frac{{50 \times {{10}^{ - 6}}}}{{5 \times {{10}^{ - 3}}}} \times 100$

$ \simeq 1\Omega $

Hence. the choices $( 3)$ and $( 4)$ are not contect.