Trioxonitrate (V) acid is not used for preparing hydrogen gas from metals because it

Trioxonitrate (V) acid, also known as nitric acid, is not used for preparing hydrogen gas from metals because it is strongly oxidizing. This means that it readily gives up oxygen to other substances, including metals. When nitric acid reacts with metals, it can produce metal nitrates instead of hydrogen gas. In addition, nitric acid can also react with the hydrogen gas produced, forming water and nitrogen oxides. Therefore, other acids, such as hydrochloric acid or sulfuric acid, are used for preparing hydrogen gas from metals as they do not have such strong oxidizing properties.