why Pluto is no longer in the list of planet?

Answer 1

Although there are many reasons, the main reason is that each planet is required to have its own unique orbit but the orbit of Pluto overlaps with that of Neptune.

A new class of celestial bodies was created called planetoids or dwarf planets. It is a size range that small planets like Pluto fell into. Its just an arbitrary definition apparently. Also it takes away the discovery of a planet by an American which is a well hated country.

The parameters for planet status considered were:

Size (because size matters now)

an orbit relatively clear of other bodies (not counting Trojans)

an orbit in the ecliptic plane (Pluto is not in the ecliptic)

Spherical shape (Pluto is spherical)