A microammeter has a resistance of $100\Omega$ and full scale range of $50\mu A$. It can be used as a voltmeter or as a higher range ammeter provided a resistance is added to it. Pick the correct range and resistance combination (s)

For option (3)

 To increase the range of ammeter a parallel resistance (called shunt) is required which is given by

$S=\left(\frac{i_g}{i-i_g}\right)G$

$S=\left(\frac{50\times {10}^{-6}}{5\times {10}^{-3}-50\times {10}^{-6}}\right)\left(100\right)=1\Omega$

For option (2)

To change it in voltmeter, a high resistance $R$ is put in series, where $R$ is given by $R=\frac{V}{i_g}-G$

$R=\frac{10}{50\times {10}^{-6}}-100=200k\Omega$

Therefore, options (2) and (3) are correct.