"Everyone knows what a/the proton is" [duplicate]

Possible Duplicate:
Are there any simple rules for article usage (“a” vs “the” vs none)

Which is correct?

1. Everyone knows what a proton is.
2. Everyone knows what the proton is.
3. Everyone knows what proton is.

Everyone knows what a proton is.

This is the most-used construct.

Everyone knows what the proton is.

This structure is a bit old-fashioned for general use, but is commonplace in scientific contexts.

Everyone knows what proton is.

This is ungrammatical. A correct way to say it is everyone knows what protons are.

Option 2 seems to emphasize "proton" as an ontological value. Option 3 sounds more abstract than 1, in the sense that "proton" could be a quality and not a noun, as in the case of "a proton". I'd say that being right or wrong depends on what you are writing. Withouth the specific context, any of them could be right.