Question

Which metal cannot be used to prepare hydrogen by the action of an acid?

Answer 1

....Since copper is less reactive than hydrogen, it is not able to displace hydrogen from dilute acids. The other metals being more reactive will displace hydrogen.....

Ya here is u are answer..

Answer 2

Explanation:

In the laboratory Hydrogen is commonly prepare from metals by the action of the acid.  Some metals such as Potassium, Sodium, Magnesium which are reacted with dilute $\bold{\mathrm{H}_{2} \mathrm{SO}_{4}}$ and HCl to produce Hydrogen, while some other metals such as Aluminum, Copper, Mercury which are not reacted with $\bold{\mathrm{H}_{2} \mathrm{SO}_{4}}$and HCl to produce Hydrogen. This quality of metals in the preparation of hydrogen by the reaction of acid depends on the reactivity series of the metals.