The correct answer is option 3, Pluto.

Pluto lost its status as a planet in recent years. This decision was made by the International Astronomical Union (IAU) in 2006. Prior to this, Pluto had been considered the ninth planet in our solar system. However, the IAU redefined the criteria for what qualifies as a planet, and Pluto no longer met those criteria.

The main reason behind Pluto`s reclassification was its size. According to the new criteria set by the IAU, a planet is defined as a celestial body that orbits the sun, is spherical in shape, and has cleared its orbit of other debris. Pluto fits the first two criteria, but it does not meet the third requirement. Its orbit is shared with other objects in the Kuiper Belt, a region beyond Neptune that is populated by icy bodies.

As a result, Pluto was downgraded to the status of a "dwarf planet." This means that it is not considered a full-fledged planet but is still recognized as an important object in our solar system. Pluto`s reclassification sparked some controversy and debate among scientists and the general public. However, the decision by the IAU remains the official classification.