Assertion : The planets move slower, when they are farther from the Sun than when they are nearer.

Reason : Angular Velocity of a planet is a constant quantity. 

By Kepler's law of areas, the line that join any planet to the Sun sweeps equal areas in equal intervals of time as shown in figure. 

The areal velocity of the planet around the sun is constant. To keep the areal velocity constant, the linear speed of the planet goes on changing. The linear speed is more, when the planet is close to the Sun and less, when it is away from the Sun.