"(1) a satellite moving around Earth in a circular <span>orbit" is the only option from the list that describes an object in equilibrium, since velocity and gravity are working together to keep the orbit constant. </span>
Oxidation number is the charge.
Since they do not stick after collision hence collision is elastic. In elastic collision, both momentum and kinetic energy is conserved because in this type of collision, first body deforms but then quickly regains its former shape and transfers its kinetic energy to the second pluck.
So kinetic energy is conserved.