Non-stoichiometric hydrides are produced by:

Non-stoichiometric hydrides are typically formed by transition metals that can absorb hydrogen without a fixed composition. Palladium and vanadium are well-known examples. In contrast, lithium forms ionic stoichiometric hydrides (LiH), nitrogen and fluorine form covalent stoichiometric hydrides (NH3, HF), and carbon forms hydrocarbons (stoichiometric). Nickel can form some non-stoichiometric hydrides but is not as characteristic as palladium and vanadium; moreover, carbon in option D is incorrect.