can we say " no thanks" instead of " u are welcome" ?

"no thanks" is used when u politely want to refuse something
"you're welcome" is used when someone thanks u for something or when they are grateful to u for something
So no, they cannot be interchanged, they have different meanings.

No, they mean different things. "No thanks" is a polite way of saying "no" when someone offers you something, while "you're welcome" is a response to "thank you."

"Do you want some food?"
"No thanks, I don't want any."

"Thank you."
"You're welcome!"

You cannot say that, they do not mean the same thing.

Ummm. they don't mean the same thing, so, yeah, you would be misunderstood, and no, you can't use them interchangeably.

I would.
Usually your welcome is used after someone thanks you.