"Which is absolutely wrong?"
"Quel" is an adjective, not a pronoun. To replace "ce qui", you would need "lequel" (pronom interrogatif), but that would introduce ambiguity: "lequel est parfaitement faux ?" as a statement, means "which is absolutely wrong".
but as question "lequel est parfaitement faux ? " means "which one is perfectly wrong?"
I'm sorry, I still don't understand why 'lequel' is wrong here. How can a sentence with a question mark be a statement?
("lequel est parfaitement faux ?" as a statement, means "which is absolutely wrong".)
"which" is translated by "ce que", which is an indefinite relative pronoun.
- ce que = what: j'aime ce que je vois = I like what I see
- ce qui = what/which: ce qui est parfaitement faux = which is absolutely wrong.
- ce dont = of/about what/which: tu sais ce dont je parle = you know what I am talking about
- ce à quoi = to what/which: tu sais à quoi je me réfère = you know what I am referring to
In the above examples, ce is accompanied by a relative pronoun (que/qui/dont/quoi) and stands roughly for "the thing": I like the thing that I see; I know the thing that I miss; you know the thing that I am talking about, etc. "ce" is used as an antecedent of the relative clause (starting with qui/que/dont/quoi).
The form of the relative pronoun itself depends on the construction of the verb and of its function: subject (qui), direct object (que) or indirect object : "dont" is used with verbs using preposition "de" "quoi" is used with verbs using any other preposition
For further explanations: http://french.about.com/od/grammar/a/indefiniterelativepronouns.htm