Question

The metal that gives hydrogen gas upon treatment with both acid as well as base is :
(A). zinc
(B). iron
(C). magnesium
(D). mercury

Answer 1

Hint:
The metal that gives hydrogen gas upon treatment with both acid as well as base will be the one that can react with both acid as well as base. Such metals that can undergo reaction with both acids and bases are known as amphoteric metals. Some examples of such metals are zinc (${\text{Zn}}$) and aluminium ( ${\text{Al}}$).

Complete step by step answer:
Generally, metals react with acids and produce hydrogen gas but the metals do not react with bases and give off hydrogen gas.
Zinc and aluminium are the exceptions in this case. Both of them can react with acid and with base such metals are known as amphoteric metals.
Amphoteric metals are those that can react both as an acid and as a base. Many metals such as zinc, copper. Aluminium forms amphoteric oxides or hydroxides.
Let’s see the example of zinc .
(A). zinc can react with strong acid such as $HCl$ to give off ${H_2}$. The reaction can be written as :
$Zn + 2HCl \to ZnC{l_2} + {H_2}$
(B). The reaction of zinc (Zn) with a base $NaOH$ also produces hydrogen.
The reaction is :
$Zn + 2NaOH \to N{a_2}Zn{O_2} + {H_2}$
Similar is the case of aluminium (Al).
(B). The reaction of $Al$ with $KOH$ is :
$2Al + 2KOH + 6{H_2}O \to 2K\left[ {Al{{\left( {OH} \right)}_4}} \right] + 3{H_2} \uparrow $
The hydrogen gas is also liberated in this case.
Hence, the answer is option A.

Note:Not only zinc ($Zn$) and aluminium ( ${\text{Al}}$), there are several other metals that behave like amphoteric metals and can react with both acids and bases and can liberate hydrogen (${{\text{H}}_{\text{2}}}$) gas respectively.