What is use of natural wair in a.c. power supply . When natural has no voltage when we touch live and natural wair why sort these

@ ajay 
the neutral is the return path for current in single wire districution system and connected to the ground , this is called as single wire earth return . 
the neutral allow unused current to return to the feeder transformer generally located at the substation for redistribution of unused current , 
if the neutral didnot exist the distribution system would not be complted . 
HOPE IT CLEARS ..