Which planet experiences a 42-year day and a night, due to its unique spin?

The planet that experiences a 42-year day and night cycle due to its unique axial tilt and spin is Uranus. This unusual rotation is a result of its extreme tilt of about 98 degrees, which means that it essentially rotates on its side. This distinctive spin leads to a situation where each pole gets around 42 years of continuous sunlight followed by 42 years of darkness as the planet orbits the Sun.

This long day-night cycle significantly differentiates Uranus from most other planets in the solar system, many of which have more typical rotational axes and day lengths. The tilt of Uranus also contributes to its extreme seasonal variations, as each pole can experience prolonged periods of light and darkness during its long orbit around the Sun.

The other choices do not have this unique characteristic. For instance, Neptune has a more typical day length of about 16 hours, Mars has a rotation period similar to Earth's, and although Pluto has a long orbital period, its rotation also does not lead to such extreme conditions of day and night.