Explanation:

- Mercury: Mercury has a very slow rotation compared to its orbit around the Sun. A single day on Mercury (sunrise to sunrise) is about 176 Earth days.

- Earth: Earth has a 24-hour day, the period it takes to rotate once on its axis.

- Pluto: Pluto, being a dwarf planet, has a rotation period of about 6.4 Earth days.

- Alpha Centauri: Alpha Centauri is not a planet but a star system, so it does not have a day length like planets do.

Correct Answer: Option 1, Mercury has the longest day in the Solar System.