Which planet has a day length of 176 Earth days?

Mercury has a unique rotational period that results in a day lasting approximately 176 Earth days. This lengthy day arises from Mercury's slow rotation on its axis coupled with its relatively short orbital period around the Sun of about 88 Earth days. As Mercury spins slowly, it takes a long time to complete one rotation, which means that one day on Mercury (from one sunrise to the next) is significantly longer than on Earth.

In contrast, Earth has a day length of 24 hours, and Venus has a day that is about 243 Earth days, making it one of the longest in the solar system. Titan, which is a moon of Saturn, has a rotation period that matches its orbital period around Saturn, resulting in a 15.9 Earth-day cycle. Therefore, the distinctive characteristic of Mercury's day length sets it apart, making it the correct answer to this question about planetary day lengths.