A voltmeter of resistance $150 \Omega$ is connected across A and B in the given circuit. The reading of voltmeter will be:

15 V

The correct answer is Option (3) → 15 V

As 100 Ω and $R_v$ are in parallel,

$\frac{1}{R_{total}}=\frac{1}{100}+\frac{1}{R_v}$  [$R_v$ = Resistance of voltmeter]

$R_{total}=\frac{100 \times 150}{100 + 150} = \frac{15000}{250} = 60Ω$

$R_{AC}=R_{total}+100$

$=160V$

Using Ohm's law,

$I=\frac{V}{R_{AC}}$

$=\frac{40}{160}=\frac{1}{4}A$

Resistance Across galvanometer is,

$∴V_{AB}=60×\frac{1}{4}=15V$