Given,

emf of the cell, $V=5 \mathrm{V}$

The voltmeter$\left(200 \mathrm{\Omega }\right)$ and $100 \mathrm{\Omega }$ resistor are in parallel and their equivalent will be in series with the another $100 \mathrm{\Omega }$ resistor.

The equivalent resistance of the given network is

$R_{\mathrm{eq}}=100+\left(\frac{100\times 200}{100+200}\right)$

$R_{\mathrm{eq}}=100+\frac{200}{3}=\frac{500}{3} \mathrm{\Omega }$

Current through the circuit is,

$i=\frac{V}{R_{\mathrm{eq}}}=\frac{5}{\left({\displaystyle \frac{500}{3}}\right)}=\frac{3}{100} \mathrm{A}$

The voltage reading of the voltage across $100 \mathrm{\Omega }$ resistor connected with voltmeter, which is same as the potential difference of equivalent resistance of $\frac{200}{3} \mathrm{\Omega }$.

$V\text{'}=\frac{3}{100}\times \left(\frac{200}{3}\right)=2 \mathrm{V}$.