The correct answer is option 1, which is 0.

To understand why, let`s consider the definition of average velocity. Average velocity is calculated by dividing the total displacement of an object by the total time taken.

In this scenario, the car starts from Bengaluru and goes 50 km towards the south. Then, it immediately turns around and returns to Bengaluru. Since the car ends up at its starting point, the total displacement is 0. This is because displacement is a vector quantity that represents the change in position of an object in a particular direction. In this case, the displacement of the car is zero because it starts and ends at the same position.

Given that the total displacement is 0 and the time taken for the round trip is 2 hours, we can divide 0 by 2 to obtain the average velocity. Any number divided by 2 is 0, therefore the magnitude of the average velocity for this round trip is 0.

Therefore, option 1 is the correct answer.