Question

$Zn + 2HCl \rightarrow ZnC{ l }_{ 2 } + { H }_{ 2 }\uparrow$
The above reaction is an example of:
(A) Combination reaction
(B) Double displacement reaction
(C) Displacement reaction
(D) Decomposition reaction

Answer 1

Hint: When one atom or a set of atoms are displaced by another atom in a molecule , then it is known as displacement reaction. The more reactive element displaces the less reactive element from the compound.

Complete answer:
There are basically five types of reactions:
1. Combination Reaction: When two or more elements or compounds combine to form a single compound, then it is known as combination reaction.

$A + B \longrightarrow AB$

2. Decomposition Reaction: When a single compound breaks down into two or elements or compounds, then it is known as decomposition reaction.

$AB \longrightarrow A + B$

3. Displacement Reaction: When one atom or a set of atoms are displaced by another atom in a molecule , then it is known as a displacement reaction.

$AB + C \longrightarrow AC + B$

4. Double Displacement Reaction: When two reactants exchange ions to form two new compounds, then it is known as double displacement reaction.

$AB + CD \longrightarrow AC + BD$

5. Combustion Reaction: When a substance reacts with the oxygen gas, and releases energy in the form of heat and light, then it is known as combustion reaction.

$C{ H }_{ 4 } + { O }_{ 2 } \longrightarrow C{ O }_{ 2 } + { H }_{ 2 }O$

Now, according to the definition of the reactions, the given reaction, i.e.,
$Zn + 2HCl \rightarrow ZnC{ l }_{ 2 } + { H }_{ 2 }\uparrow$
is a displacement reaction. Hence, (c) is the correct option.

Note: Displacement reaction occurs only if certain condition is met:
Only a highly reactive metal in the reactivity series displaces the low reactive metal. Displacement reactions are slow in rate.