"Which one is it?"
Translation:Laquelle est-ce ?
Ce is unspecified, unknown or something/somebody new in the context C'est qui?. Il / elle can be something or somebody but it is already something you know of: Où est mon manteau? Oh, il est là!
Both Lequel est-ce? (male) and Laquelle est-ce? (female) are accepted as correct answers.
Note: If you have a typo in your answer, DuoLingo will guess which one you were trying to type (Lequel or Laquelle) and suggest a correction based on that guess. Sometimes DuoLingo makes a wrong guess, and this can lead to some (in my opinion, uneccissary) confusion.
For Example: In the beginning, I typed Laquelle with a typo and Duo suggested the correct answer was Lequel. This led me (wrongly) to believe Laquelle is wrong when in fact it is perfectly fine (I just had a typo). I guess that Duo thought I was trying to type Lequel and suggested a correction accordingly.
I write ca but it said it was correct but corrected to ce. Does that mean ca is okay?