Question

Why pluto is decleared as a draft planet?

Answer 1

Because it has not cleared the neighborhood around its orbit, Pluto isconsidered a dwarf planet. It orbits in a disc-like zone beyond the orbit of Neptune called the Kuiper belt, a distant region populated with frozen bodies left over from the solar system's formation.

Answer 2

Pluto become a dwarf planet because its size is comparatively too small and sometimes it violates the rule by getting into the orbit of neptune and its distance from the sun is more and pluto 

and there were many bodies similar to the size of pluto and some of them were bigger than pluto and they had certain different characteristics therefore the scientists decided to consider pluto as dwarf planet 

there would be chances of collision of pluto and neptune but  stable orbital resonance with Neptune prevents them from colliding