In conversation is de rien sometimes shortened to rien?

Answer 1

'de rien' is a fixed expression that you use in reply to 'thank you' (as 'no problem' or 'you're welcome'). That form is never shortened. But rien ('nothing') is also used on its own: "qu'est ce que tu fais ? Rien" (what are you doing? Nothing.")

Answer 2

Yes, de rien can be shortened to rien in conversation. It is a more casual and informal way of saying "you're welcome" in French. Both expressions are used to respond to someone who has thanked you for something.