How many hydrogen in salt?
"Common salt", with the chemical formula NaCl, does not contain any hydrogen. The much larger chemical class of "salts" includes some examples that do contain hydrogen, for example the ammonium salts.
Copper is less reactive than hydrogen (look at the reactivity series), so will not take the place of hydrogen in an acid to form a salt and hydrogen. Metals which are more reactive than hydrogen will take the place of hydrogen to form a salt + hydrogen gas. For example: Magnesium + hydrochloric acid --> magnesium chloride + hydrogen
The crystals of salt provides nucleation centers where bubbles of oxygen form and this accelerates the rate of decomposition of the hydrogen peroxide into water and oxygen. The salt does not participate in any chemical reaction (not even as a catalyst). The water in the hydrogen peroxide dissolves some of the salt crystals, reducing the number of of nucleation centers (gradually slowing the rate of decomposition of the hydrogen peroxide into water and oxygen back…