If no.of turns are increased in a moving coil galvanometer the current sensitivity Inc.but there`s a Dec.in voltage sensitivity hence the effect is nullified??

Current sensitivity does not depend upon resistance(R), whereas voltage sensitivity does, as evident from their expressions. Current sensitivity can be increased by increasing the number of turns of the coil. However, this increases the resistance of the coil also(R is proportional to length of conductor). Since voltage sensitivity decreases with increase in resistance of the coil, the effect of increase in number of turns is nullified in the case of voltage sensitivity. Hence, there is no increase in voltage sensitivity.