how China pegging dollar1 to rmb8.20 cause USA economy to chaos?

Answer 1

It won't. What it does is make Chinese made goods artificially cheap in the US, so China can sell more here. Some people would like to see China lift exchange rate restrictions, because it would make Chinese goods more expensive and make US goods more attractive.
At present, the US is at a competitive disadvantage and some politicians think that removing the dollar peg and letting the Chinese renminbi become more expensive will solve the problem.
As far as causing chaos....No.