This is probably the most common question we receive - except for the lemon rice soup part. You're the first person ever to have burned that!
If you get to it quickly, that is, before the burnt taste saturates the whole dish, get it off the heat. If you can do it safely, put the bottom of the pan in a larger container of cold water or tilt the pan a bit under a faucet, so that the cold water runs down the outside of the pan and across the bottom. Then pour or spoon the soup into another pan. Don't scrape off anything that's stuck to the pan. Finally, taste it.
If you were quick enough, you may have managed to keep the burnt taste in the first pan. If not, there's nothing you can do. Throw out the rest of the dish, go out to eat and enjoy someone else's lemon rice soup, and take comfort in the fact that this happens to everyone.