Recently, which one of the following lost the status of a planet ?

Pluto was discovered in 1930 and was long considered the ninth planet of our solar system [1][t1]. However, in August 2006, the International Astronomical Union (IAU) adopted a formal definition of a planet that required a celestial body to orbit the Sun, possess sufficient mass for hydrostatic equilibrium (a nearly round shape), and have cleared the neighborhood around its orbit [c1][t3]. While Pluto meets the first two criteria, it fails the third because it resides in the Kuiper Belt, a region filled with icy debris [c1][t4]. Consequently, the IAU reclassified Pluto as a 'dwarf planet' [t6][t8]. The other options—Mercury, Neptune, and Uranus—retain their status as full-sized planets, with Mercury classified as a terrestrial planet and Uranus and Neptune as ice giants [c2][c5][t3].

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 2: The Solar System > Kuiper Belt, Pluto, and Charon > p. 33