The scale of a galvanometer of resistance 100 Ω contains 25 divisions. It gives a deflection of one division on passing a current of 4 × 10^-4 A. The resistance (in ohm) to be added to it, so that it may become a voltmeter of range 2.5 V is:

150

Maximum current possible in galvanometer = 25 × 4 × 10^-4 A = 10^-2 A

So, $10^{-2}=\frac{25}{100+R}$

100 + R = 250

Resistance, R = 150 Ω