Question

Which of the following are displacement reactions?

• A. $Cu\left(s\right)+2AgN{O}_3\left(aq\right)⟶2Ag\left(s\right)+Cu\left(N{O}_3{)}_2\right(aq)$
• B. $Ca\left(s\right)+2H_{2}O\left(l\right)⟶2NaOH\left(aq\right)+H_2\left(g\right)$
  
• C. $2Pb\left(N{O}_3{)}_2\right(s)\to 2PbO(s)+2N{O}_2(g)+\frac{1}{2}{O}_2(g)$
• D. $N_2\left(g\right)+O_2\left(g\right)\to 2NO\left(g\right)$

Answer 1

Answer: (A), (B)

$Ca\left(s\right)+2H_{2}O\left(l\right)⟶2NaOH\left(aq\right)+H_2\left(g\right)$


Theory :
In displacement reaction, an atom or ion of a compound is replaced by an atom or ion of some other element.
Displacement reactions :
$X+YZ⟶XZ+Y$
It os basically two types :
1. Metal displacement reaction : One metal is displaced by some other metal in the elemental state.
Example :
a) $Cu\left(s\right)+2AgN{O}_3\left(aq\right)⟶2Ag\left(s\right)+Cu\left(N{O}_3{)}_2\right(aq)$
2. Non-metal displacement reaction : Here one metal or a nonmetal displaces another nonmetal from its compound.
Example :
b) $Ca\left(s\right)+2H_{2}O\left(l\right)⟶2NaOH\left(aq\right)+H_2\left(g\right)$
So both (a) and (b) are the example of displacement reactions.

In option (c) the reaction involves the breaking down of lead nitrate into three components. Therefore, this is categorized under decomposition redox reaction.
In option (d), the compound nitric oxide is formed by the combination of the elemental substances, nitrogen and oxygen. So it is an example of combination reaction.