Answer : The softball loses kinetic energy and gains potential energy. Explanation :
Mechanical energy is the sum of the potential energy and the kinetic energy.
Kinetic energy of an object is possessed by virtue of its motion.
Potential energy of an object is possessed by virtue its height under the action of gravity.
When the softball is hit high into the air. As it rises, the softball loses kinetic energy and gains potential energy. Hence, the total energy remains constant.
Hence, the correct option is (b).