Question

Which metal cannot displace hydrogen from dilute acids?

• A. $Cu$
• B. $Mg$
• C. $Zn$
• D. $Na$

Answer 1

The correct option is A

$\mathrm{Cu}$

Electrochemical series or the metal reactivity series is the arrangement of the metals in the decreasing order of their reactivity.

Metals placed above Hydrogen (${\mathrm{H}}_2$) in the electrochemical series are more reactive than Hydrogen (${\mathrm{H}}_2$). As a result, they can displace Hydrogen (${\mathrm{H}}_2$).

Explanation of the correct option:

• The metals which are present below the hydrogen in the reactivity series react with dilute acid and produce hydrogen gas. (We need to tell about reaction it's given in the guidelines)

(A) Copper ($\mathrm{Cu}$): Copper ($\mathrm{Cu}$) is placed below the Hydrogen (${\mathrm{H}}_2$) in the electrochemical series due to which it cannot displace Hydrogen (${\mathrm{H}}_2$) from dilute acids.

Explanation of the incorrect option:

(B) Magnesium ($\mathrm{Mg}$): Magnesium ($\mathrm{Mg}$) is placed above the hydrogen in the electrochemical series due to which it can displace Hydrogen (${\mathrm{H}}_2$) from dilute acids because Magnesium ($\mathrm{Mg}$) is more reactive than Hydrogen (${\mathrm{H}}_2$).

(C) Zinc ($\mathrm{Zn}$): Zinc ($\mathrm{Zn}$) is placed above the hydrogen in the electrochemical series due to which it can displace Hydrogen (${\mathrm{H}}_2$) from dilute acids because Zinc ($\mathrm{Zn}$) is more reactive than Hydrogen (${\mathrm{H}}_2$).

(D) Sodium ($\mathrm{Na}$): Sodium ($\mathrm{Na}$) is placed above the hydrogen in the electrochemical series due to which it can displace Hydrogen (${\mathrm{H}}_2$) from dilute acids because Sodium ($\mathrm{Na}$) is more reactive than Hydrogen (${\mathrm{H}}_2$).

Therefore, the correct option is (A).

Correct approach:

Explanation of the correct option:

Metals that are present below hydrogen in the activity series of metals are less electropositive than hydrogen and they cannot displace hydrogen from the dilute acid solution hence, they do not react with the dilute acid solution.
Metals that are present below hydrogen in the activity series do not react with acids and release hydrogen ions

(A) talk about the option with a suitable reaction

The explanation for the incorrect option:

Metals that are present above hydrogen in the activity series of metals are more electropositive than hydrogen and can replace hydrogen from the dilute acids, hence they react with acids and generate hydrogen gas.

(no need of rewriting the same thing for all incorrect options)

NOTE: Avoid writing formulas and Elements symbols everywhere. It is making answers look weird