The physical quantity of the following that is not conserved in case of a planet revolving in an orbit is

In a planet revolving in an orbit, total mechanical energy (kinetic energy + potential energy) is not conserved. As the planet revolves around the sun, it loses energy due to the gravitational force acting on it, causing its orbit to gradually decrease. This loss of energy is due to the emission of gravitational waves or the radiation of energy in the form of light, heat or any other form. Eventually, if the planet is close enough to the sun, it will lose enough energy to be captured by the sun, or if it is far enough, it will lose enough energy to escape the solar system.

On the other hand, angular momentum is conserved in the case of a planet revolving in an orbit, as long as no external torque acts on it.  This is due to the law of conservation of angular momentum, which states that the angular momentum of a system remains constant if no external torque acts on it.

 Areal velocity and Kinetic energy are also conserved in this scenario.

Hence the correct answer is total energy.