Question

Which of the following would evolve hydrogen from dilute nitric acid?
A.Magnesium
B.Iron
C.Copper
D.zinc

Answer 1

Hint: We know that it is the property of the metal that when it comes in contact with acid, hydrogen gas is released. The evolution of hydrogen gas when nitric acid reacts with metal is a displacement reaction in which the metal ion will be replaced by the one hydrogen of the monoacid i.e. nitric acid. Acid is an oxidizing agent which will act as proton donor, so hydrogen is replaced by metal.


Step by step answer: acid contains only one hydrogen atom which can be replaced by metal, non-metal or organic compound. Monoacidic acid $$HN{O}_3$$have one hydrogen which will replace metal ,the metal from the options are magnesium because it has stronger ability to donate electron and convert into positive ion as it belongs to s-block in periodic table and nitric acid have a tendency to accept the electron and form a bond with metal ion as it is a good oxidizing agent.

As you can see, other options are transition metals which will try to form complex via coordinate covalent bond hence instead of emission of hydrogen gas stable complex may be obtained. Transition metals have many oxidation states therefore, there is a possibility that (if acid is strong)$$N{0}_2$$ and (if acid is dilute )$$NO$$ gas may be released instead of hydrogen gas.

These gases cause pollution in the atmosphere.
The reaction of magnesium with nitric acid is as follows:$$Mg+HN{O}_3\to Mg(N{O}_3{)}_2+H_{2(g)}$$

The reaction of transition metal with nitric acid is as follows: $$M+xHN{O}_3\to M(NO2{)}_2+xNO+XN{O}_2$$

Hence, the answer will be option (A) Magnesium.

Note: Look at the options carefully to eliminate the useless options and do not get confused between the Magnesium atom of s-block and Manganese atom of d-block.