The force acting on the ball is the same than the ball acts on the floor at the moment of hitting but in the reverse direction. So the ball produces a force downwards and the floor makes the same force in value but upwards.
Then the value of the force that impulses the ball upward is: F = m * a
where F is force or impulse, m is mass of the ball and a is acceleration (9.8 m/s2)
F = 1.2 kg * 9.8 m/s2 = 11.76 kg*m/s2 = 11.76 Newtons (upwards)
