The ball went up, reached zero velocity and then fell back to the ground. All this happened in 2 seconds. Since the acceleration and deceleration is same in magnitude, that is equal to acceleration due to gravity (g), the ball took 1 sec in upward journey and 1 sec in downward journey.
Distance travelled in 1 sec can be given as:
S = 1/2 gt^2 = 1/2 x 9.81 x 1^2 = 4.9 meter.
Hope this helps.