Assault in the first degree

(1) A person is guilty of assault in the first degree when: (a) He intentionally causes serious physical injury to another person by means of a deadly weapon or a dangerous instrument; or (b) Under circumstances manifesting extreme indifference to the value of human life he wantonly engages in conduct which creates a grave risk of death to another and thereby causes serious physical injury to another person. (2) Assault in the first degree is a Class B felony.