I got a Jade plant a couple of days ago it was healthy and strong with nice plump leaves, but today I noticed it is all rotten and mushy, I gave it a little water when I first got it and repotted it, and left it in the sun. What would couse it ito rot like this, and is there any way to save it?

I am a bit surprised that your Jade has reacted so severely in such a short period of time. It may have already had a problem before you purchased it.

Repotting was not a good idea because Jades have fine root systems that are best left undisturbed. In a larger pot, it is at greater risk of root rot. If you placed outside in the direct sun, that is also not a good idea. A sunny window inside is a much better location.