What is which in French?

Answer 1

Correct, I mean, "merci"

In English, the word "Which" is used in both interrogative and relative pronoun.

If you're try to use "which" (or "that" as an opposite), you say "lequel" as in interrogative and "qui" as in relative.

An example of the word is one of these:

Interrogative:

Lequel des oiseaux est Aves?

Which one of the bird are Aves?

For relative:

Il doit y avoir une conférence de la Marin qui se tiendra à Moscou.

There must be a conference for marine war which will hold in Moscow.

Answer 2

Lequelle.