It is the eighth planet sometimes nineth?

Answer 1

The outermost planet in our solar system, Neptune, is often referred to as the eighth planet. When Pluto was considered a planet (prior to 2006) during its orbit it would cross inside the orbit of Neptune making the latter the outermost planet.

Answer 2

The eighth planet in our solar system is Neptune, while the ninth planet used to be Pluto. However, Pluto was reclassified as a dwarf planet in 2006, so currently, Neptune is considered the eighth and last major planet in the solar system.