What is the function of the catalytic converter installed in a vehicle's exhaust system?

1. To reduce exhaust noise to an acceptable decibel level.
2. To convert harmful exhaust gases (HC, CO, and NOx) into less harmful products (H2O, CO2, and N2).
3. To cool down the hot exhaust gases before they reach the muffler.
4. To filter soot and ash particles mechanically.