Uranus takes longer than Mars to revolve around the sun because Uranus is further away from the sun than Mars so it won't travel as fast as Mars due to the distance.
Mars is way closer than Uranus. Planets that are farther away from the Sun have longer orbits. For Uranus to go around the Sun, it takes around 84 Earth years. Mars completes its orbit around the Sun in about 1.8 Earth years.
