Formal:
* De rien: This is the most common and polite way to say "you're welcome" or "it was nothing."
* Il n'y a pas de quoi: This translates literally to "there is nothing for which" and is a slightly more formal and elaborate way to say "it was nothing."
Informal:
* Pas de problème: This means "no problem" and is a very casual way to say "it was nothing."
* C'est rien: This is a direct translation of "it's nothing" and is also a common way to respond to a thank you in an informal setting.
* Pas du tout: This means "not at all" and is another way to say "it was nothing" in an informal context.
Example:
* A: Merci pour votre aide! (Thank you for your help!)
* B: De rien! (You're welcome!)
The best way to choose the right phrase depends on the specific situation and your relationship with the person you are talking to.