Answer 1

Well, let's see here...

• Ekans
• Arbok
• Seviper
• Snivy
• Servine
• Serperior

Now, a mention for these Pokemons:

• Huntail
• Gorebyss
• Eelektrik
• Eelektross

These, being Eel, or Eel-like Pokemons, are often confused as snake-like.
Eel, a snakelike fish. Eels may look like snakes, but they aren’t related to those slithery reptiles at all. Eels are actually fish.
Science source
Pokemon Source

Answer 2

This is according to the Pokemon Species.

• Dunsparce (Land Snake Pokemon)
• Ekans (Snake Pokemon)*
• Onix (Rock Snake Pokemon)
• Steelix (Iron Snake Pokemon)
• Servine/Snivy (Grass Snake Pokemon)* *
• Seviper (Fang Snake Pokemon)

Source:
http://bulbapedia.bulbagarden.net/wiki/List_of_Pok%C3%A9mon_by_species
Looked through the whole list.

*= Arbok may also be considered a Snake
* *= Serperior may also be considered a Snake

Trivia: Ekans is 'snake' backwards, and Arbok is 'kobra' backwards.

Answer 3

Arbok
Ekans
Onix
Serperior
Snivy
Seviper
Dunsparce
Servine
Milotic
I looked through the Pokedex