Which of these Pokemon was the first Pokemon?

It actually depends on what you mean by the first Pokemon? Arceus is said to have created the Pokemon, Bulbasaur is the first in the Pokedex, Mew may be the ancestor of Arceus and as for Rhydon, it was apparently the first one to have been created so take your pick, which ever one suites your question.

Well I know its not arceus because he's from way later in the seties . now rhydon new and bulbasuar are all from the original game but I know for a fact its not mew because new was a event Pokemon released after a the game was. And I know for a fact that the starters are one of the first Pokemon so I'm going to guess bulbasuar

A.) Bulbasaur.

Well that depends on how you look at it, didn't Arceus create the pokemon world? Which would make him the very, very 1st pokemon. Otherwise in our world the creators of pokemon made Bulbasaur 1st. The 1st pokemon created for every generation is usually the starter pokemon at the beginning of the games.

All of them depending of how you view it.

I consider rhydon to be first

Mew

E. None of the above.

Umm haha guys! The correct answer is all!.
Rhyhorn was the first to be designed, bulbasaur is the first in the pokedex, mew's pokedex states it made the other Pokemon so it'd have to be "first" and arceus is basically like a god if your read his dex entries, so in a way he came first.