Question

why is pluto no longer considered to be a planet

Answer 1

Because it is very far from sun. And it is very cold and considered as dwarf planet.

Another fact is that Pluto id smaller than Russia.
Yes, it's true.

Answer 2

The distance cue ball of a frozen world known as Pluto has always been a space oddity (it's smaller than the Earth's moon and follows a squashed orbit around the sun that takes 248 years). When astronomers began discovering other heavenly bodies rivaling tiny Pluto in size, they started to rethink their definition of a planet. Pluto no longer made the cut.

Hope it helps you :)