* If you're talking about the soda: Mixing 7 Up (or any carbonated beverage) with salt will create a fizzy, salty solution. It won't cause any dramatic chemical reactions, but it's not likely to be very tasty.
* If you're talking about the number "7" and "up": These are concepts, not physical substances, so you can't actually mix them.
Important note: It's never a good idea to mix chemicals or substances without proper knowledge and safety precautions. If you're curious about chemical reactions, stick to safe, controlled experiments or consult a science expert.
