What is the difference between a direct current and an alternating current? How many times does $AC$ used in India change direction in one second?

(N/A) Direct current $(DC)$ flows in only one direction throughout the circuit. In contrast,alternating current $(AC)$ reverses its direction periodically.
The frequency of $AC$ in India is $50 \, Hz$,which means it completes $50$ cycles per second.
Since the current changes its direction twice in each cycle,the total number of times it changes direction in one second is $2 \times 50 = 100$ times.