Question

any celestial object going round the sun is considered a planet .then why pluto has now been dropped from the status of a planet

Answer 1

Um...
It crosses Uranus's(Or Neptune?) orbit.It is closer to the kuiper belt.And it's too small.

Also according to your condition,asteroids and satellites would also technically be 'planets'.

Answer 2

The Condition that "any celestial object going around the sun is considered a planet" is wrong.
The condition is that the celestial object being talked about here must be at least of a particular size.
Since Pluto is too small in size To be considered a planet, it has been eliminated from the status of the planet