All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
The ruling on this differs according to whether he did it intentionally or by mistake and according to the extent of the crime resulting thereof, whether throwing the acid leads to killing the victim or damaging part of his body. The reference in such cases is the Islamic (Shariah) court.
Allah knows best.