The number of turns of the coil of moving coil galvanometer is increased in order to increase current sensitivity by 50%. The percentage change in voltage sensitivity of the galvanometer will be:

$\text{ Voltage sensitivity }=\frac{\text{ current sensitivity }}{\mathrm{G}}$
G = resistance of the  galvanometer
$\mathrm{Current} \mathrm{sensitivity}=\frac{\mathrm{NAB}}{\mathrm{c}}$
As current sensitivity increases by 50%, no of turns increasing by 50% 
$\therefore$ voltage sensitivity remains constant as G also increases by 50%