Explain the laboratory preparation of dihydrogen.

(N/A) In the laboratory,dihydrogen is prepared by the reaction of granulated zinc with dilute hydrochloric acid:
$Zn(s) + 2H^{+}(aq) \longrightarrow Zn^{2+}(aq) + H_{2}(g)$
It can also be prepared by the reaction of zinc with aqueous alkali,such as sodium hydroxide:
$Zn(s) + 2NaOH(aq) \longrightarrow Na_{2}ZnO_{2}(aq) + H_{2}(g)$
In this reaction,sodium zincate $(Na_{2}ZnO_{2})$ is formed as a byproduct.