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

The correct metal displacement reaction is:
${\mathrm{Cr}}_2{O}_3+2\mathrm{Al}\to {\mathrm{Al}}_2{O}_3+2\mathrm{Cr}$

Step-by-Step Explanation:

1. Understanding Metal Displacement Reactions:
A displacement reaction occurs when a more reactive element displaces a less reactive element from its compound. In the specific case of a metal displacement reaction, a more reactive metal in its elemental state displaces a less reactive metal from its oxide, halide, or salt solution.

2. Analyzing the Correct Option:
In the reaction:
${\mathrm{Cr}}_2{O}_3+2\mathrm{Al}\to {\mathrm{Al}}_2{O}_3+2\mathrm{Cr}$
Here, Aluminum ($\mathrm{Al}$) and Chromium ($\mathrm{Cr}$) are both metals. According to the electrochemical / reactivity series of metals, Aluminum is highly reactive compared to Chromium. Therefore, Aluminum acts as a reducing agent, displacing Chromium from its oxide (${\mathrm{Cr}}_2{O}_3$) to form Aluminum Oxide (${\mathrm{Al}}_2{O}_3$) and elemental Chromium ($\mathrm{Cr}$). Since one metal displaces another metal, this is a true metal displacement reaction.

3. Comparing with the Other Types of Reactions:
Let us analyze why the other options do not qualify as metal displacement reactions:
• Decomposition Reactions: Reactions such as:
$2\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2\to 2\mathrm{PbO}+4{\mathrm{NO}}_2+O_2$
and
$2{\mathrm{KClO}}_3\to 2\mathrm{KCl}+3O_2$
are thermal decomposition reactions because a single reactant breaks down into multiple products when heated. No displacement occurs.
• Non-metal Displacement Reaction: In the reaction:
$3\mathrm{Fe}+4H_{2}O\to {\mathrm{Fe}}_3{O}_4+4H_2$
the metal Iron ($\mathrm{Fe}$) displaces Hydrogen (which is a non-metal) from water ($H_{2}O$). Therefore, this is classified as a non-metal displacement (hydrogen displacement) reaction, not a metal displacement reaction.