Yes, but if you want to simply say, "Why?", then it would be more common to say "What for?". John: Turn off the light when you leave the room. Alex: What for?

- What for = why = for what purpose or reason? 'What is this tool for?' 'I need to see a doctor.’ ‘What for?’ - For what: it doesn't mean 'why'. Instead, it is used to inquire about the specific use of something: "I'm giving you this ticket." "For what? A movie, a concert, a ball game? "What for?" (=why?)

This is an answer to the same question I did before, I hope it will help you: In BR English you can use either in conversation, but there is a small difference which is sometimes important. What for? = why? For what? = for what purpose? or why? Example: ‘Can I borrow your chair?’ ‘what for?’ – why? ‘for what?’ – what are you going to do with my chair?

Same meaning, it is interchangable.

I agree with Teresa.