In compressed state, a spring 3.00 meters long hanging from the ceiling has a potential energy of 2.0 joules. if the entire potential energy is used to release a ball of mass 1.2 kilograms vertically downward, then what is the kinetic energy of the ball when it reaches the ground?

We can't tell from the information in the question.

The kinetic energy of the ball when it hits the floor will be

           (the 2 joules that it got from the spring when the spring
             suddenly flung it away from the ceiling)

             PLUS

           (the gravitational potential energy the ball had
            just from being up at the ceiling) .

We don't know the total, because we don't know how high the ceiling is
above the floor.