The oxidation number of hydrogen is typically +1 when it is bonded to nonmetals. For example, in water (H2O), each hydrogen atom has an oxidation number of +1. This positive oxidation state arises because hydrogen can lose its single electron when it forms bonds with more electronegative elements.
However, when hydrogen is bonded to metals, it can have an oxidation number of -1. For instance, in metal hydrides like sodium hydride (NaH), the oxidation number of hydrogen is -1. This negative oxidation state occurs because hydrogen gains an electron from the metal, acting more like a halogen in these cases.
To summarize, hydrogen’s oxidation number is generally +1 when combined with nonmetals and can be -1 when combined with metals. It’s important to determine the context in which hydrogen is found to accurately assign its oxidation number.