Advanced Placement (AP) Chemistry Practice Exam 2025 - Free AP Chemistry Practice Questions and Study Guide

In most compounds, hydrogen has an oxidation number of +1. This is based on the common behavior of hydrogen in chemical bonding. When hydrogen forms compounds with nonmetals, such as in water (H₂O) or hydrochloric acid (HCl), it typically contributes one electron, which results in it having a +1 oxidation state. This is because it acts as a donor of one electron in these covalent bonds, reflecting its position in Group 1 of the periodic table.

While hydrogen can have an oxidation number of -1 in metal hydrides (for example, when combined with lithium in lithium hydride, LiH), the condition under which it does is less common. Thus, in the majority of compounds and situations, including organic and inorganic compounds, the oxidation state for hydrogen is consistently observed as +1.