Answer is A.
The rate at which alternating current reverses direction is called its frequency, expressed in hertz. Thus, standard household current in India is 50 Hz. AC electricity alternates back-and-forth in direction 50 times per second, according to the electrical system in the country. The charge at the ends of the wire alternates between negative (-) and positive (+). If the charge is negative (-), that pushes the negatively charged electrons away from that terminal. If the charge is positive (+), the electrons are attracted in that direction. Thus the electricity in the wire moves in one direction for a short while and then reverses its direction when the generator armature is in a different position. The direction changes twice in each cycle so that change of direction takes place after every 1/100 second.