Question

Question 18
Which of the following are combination reactions?

(i) $2{\text{KClO}}_3\stackrel{\text{Heat}}{\to }2\text{KCl}+3{\text{O}}_2$
(ii) $\text{MgO}+{\text{H}}_2\text{O}\to {\text{Mg(OH)}}_2$
(iii) $4\text{Al}+3{\text{O}}_2\to 2{\text{Al}}_2{\text{O}}_3$
(iv) $\text{Zn}+{\text{FeSO}}_4\to {\text{ZnSO}}_4+\text{Fe}$

(a) (i) and (iii)
(b) (iii) and (iv)
(c) (ii) and (iv)
(d) (ii) and (iii)

Answer 1

A reaction in which two or more reactants react together to form a single product is called a combination reaction. In reaction (ii), $\text{MgO}$ and ${\text{H}}_2\text{O}$ are combining to form ${\text{Mg(OH)}}_2$ and in reaction (iii), $\text{Al}$ and ${\text{O}}_2$ are combining to form ${\text{Al}}_2{\text{O}}_3$.

In reaction (i), $2{\text{KClO}}_3$ is undergoing thermal decomposition, hence it is a decomposition reaction whereas reaction (iv) is a single displacement reaction.

So, Option (d) is correct.