A comet orbits the sun in a highly elliptical orbit. Which of the following quantities remains constant throughout its orbits?
(i) Linear speed
(ii) Angular speed
(iii) Angular momentum
(iv) Kinetic energy
(v) Potential energy
(vi) Total energy

Comet is revolving around the Sun in elliptical path due to gravitational force between them. Torque acting on the comet is zero and thus the angular momentum of the comet will remain conserved. Also, as there is no dissipative forces are involved, total energy of the system will remain conserved.
Linear speed of the comet increases when it reaches closer to the Sun and decreases when goes farther. Due to this kinetic energy also changes. As total energy is constant, but kinetic energy is changing, potential energy is also changing.