Assertion (A) : All combination reactions are redox reactions

Reason (R) : All displacement reactions are redox reactions.

There is no necessity for every combination reaction to be redox reaction.

Ex: ${\text{CaO(s)\hspace{0.17em}+\hspace{0.17em}H}}_{\text{2}}\text{O\hspace{0.17em}}\left(l\right)\to \text{Ca}{\left(\text{OH}\right)}_2\left(aq\right)$.

In the above reaction, there is no change in the oxidation state of Ca, O and H atoms in both

reactants and products. Every displacement reaction must be a redox reaction.

Ex: $\stackrel{\left(0\right)}{\text{Zn}}\left(s\right)+2\underset{\text{dil.acid}}{\stackrel{+1}{\text{H}}\stackrel{-1}{\text{C}l}}\to \stackrel{+2}{\text{Zn}}\stackrel{-1}{\text{C}{l}_2}\left(aq\right)+{\stackrel{\left(0\right)}{\text{H}}}_{\text{2}}\left(g\right)$