Figure shows a planet in an elliptical orbit around the Sun S. Where is the kinetic energy of the planet maximum?

Here, angular momentum is conserved. According to it. At point $P_4$, the value of R is minimum and hence the velocity is maximum or KE is maximum
 In an elliptical orbit, the principle of conservation of angular momentum plays a crucial role in determining the speed and kinetic energy of a planet. According to this principle, the angular momentum of a planet remains constant throughout its motion around the Sun.