b. light wave
c. longitudinal wave
d. water wave
increases is the answer for sure
The correct answer to the question is : Mechanical energy.
EXPLANATION:
Let us consider a pendulum which is raised to certain height. The energy possessed by the pendulum at this height is gravitational potential energy.
Let the pendulum is released. Now the potential energy of the pendulum is converted into kinetic energy. At the mean point, whole of its potential energy is converted into kinetic energy.
Due to inertia, the pendulum will overshoot its mean position and will move towards its extreme position. During its movement from mean point to extreme point, the kinetic energy is converted into potential energy. At extreme point, whole of its kinetic energy is converted into potential energy.
Hence, there is only energy conversion between kinetic energy and potential.
We know that sum total of kinetic energy and potential energy is called mechanical energy.
Hence, the correct answer is mechanical energy.