$(a)$ Name two forms of energy involved while a pendulum oscillates.
$(b)$ Show with the help of a diagram that when does each type of energy attain its maximum value.
$(c)$ How do these energies vary while the pendulum oscillates?
$(d)$ Name and state the law involved.

(N/A) The two forms of energy involved are Kinetic Energy $(KE)$ and Potential Energy $(PE)$.
$(b)$ In the diagram,point $A$ represents the extreme position where $PE$ is maximum and $KE$ is zero. Point $B$ represents the mean position where $KE$ is maximum and $PE$ is zero.
$(c)$ As the pendulum moves from the mean position $(B)$ to the extreme position $(A)$,$KE$ is converted into $PE$,so $KE$ decreases and $PE$ increases. Conversely,as it moves from the extreme position $(A)$ to the mean position $(B)$,$PE$ is converted into $KE$,so $PE$ decreases and $KE$ increases.
$(d)$ The law involved is the Law of Conservation of Energy. It states that energy can neither be created nor destroyed,only transformed from one form to another. In an isolated system,the total energy remains constant.