Question

Which of the following reactions is the metal displacement reaction ? Choose the right option.

• A. $2KClO_3 {->[\Delta]} 2KCl + 3O_2$
• B. $Cr_2O_3 + 2Al {->[\Delta]} Al_2O_3 + 2Cr$
• C. $Fe + 2HCl \to FeCl_2 + H_2 \uparrow$
• D. $2Pb(NO_3)_2 \to 2PbO + 4NO_2 + O_2 \uparrow$

Answer 1

The Correct Option is B

To identify the metal displacement reaction from the given options, we need to understand what defines a displacement reaction. A metal displacement reaction is a type of redox reaction in which a more reactive metal displaces a less reactive metal from its compound.

Let's analyze each option:

1. $2KClO_3 \xrightarrow{\Delta} 2KCl + 3O_2$: This reaction is a decomposition reaction where potassium chlorate decomposes to form potassium chloride and oxygen gas. No metal displacement occurs here.
2. $Cr_2O_3 + 2Al \xrightarrow{\Delta} Al_2O_3 + 2Cr$: Here, aluminum (Al), which is more reactive than chromium (Cr), displaces chromium from its oxide (Cr₂O₃) to form aluminum oxide (Al₂O₃) and free chromium. This is a metal displacement reaction.
3. $Fe + 2HCl \to FeCl_2 + H_2 \uparrow$: This is a single displacement reaction where iron displaces hydrogen from hydrochloric acid to form iron(II) chloride and hydrogen gas. Although this involves the displacement of a non-metal (hydrogen), it is not classified purely as a metal displacement reaction as it involves an acid.
4. $2Pb(NO_3)_2 \to 2PbO + 4NO_2 + O_2 \uparrow$: This is another decomposition reaction where lead(II) nitrate decomposes to yield lead(II) oxide, nitrogen dioxide, and oxygen gas. There is no displacement of a metal here.

After considering all the options, clearly, the reaction in option 2 ($Cr_2O_3 + 2Al \xrightarrow{\Delta} Al_2O_3 + 2Cr$) is the correct example of a metal displacement reaction. Aluminum, being more reactive, displaces chromium from its compound to form aluminum oxide and free chromium.