Oxidation number of hydrogen in KH?
The oxidation number of hydrogen in potassium hydride is -1, because hydrogen has a much higher electronegativity than potassium, even though in most of its compounds hydrogen is more likely to have an oxidation number of +1.
The oxidation number of hydrogen in KH is -1, because the only oxidation number for potassium in a simple inorganic compound is +1. A hydrogen atom can complete its outer electron shell by adding one electron acquire the electron configuration of helium, and this is what happens during the formation of alkali metal hydrides such as KH.
In H2PO4-, oxygen has the formal oxidation number -2, phosphorus has the formal oxidation number +5, and hydrogen has the formal oxidation number +1. The formal oxidation numbers for oxygen in almost all oxyanions and for hydrogen in almost all acid anions have these values, so that the remaining element can be assigned a formal oxidation number by the requirement of satisfying the total electrical charge if any shown in the formula.