The planet that takes the longest time to revolve around the sun is Neptune.

Here's why:

* Orbital Period: Neptune takes approximately 165 Earth years to complete one orbit around the sun. This is due to its vast distance from the sun.

* Distance: Neptune is the farthest planet from the sun in our solar system.

* Kepler's Laws: Kepler's laws of planetary motion state that the further a planet is from the sun, the longer its orbital period will be.