Question

Most of the decomposition reactions are:
A.Exothermic
B.Endothermic
C.Reduction
D.Oxidation

Answer 1

Hint:The decomposition reactions are one of the types of redox reactions. So the decomposition reactions can be exothermic, endothermic, oxidation, and reduction. But in this question, we are supposed to favor the majority of decomposition reactions.

Complete step by step answer:
First, we will understand the redox reaction and its types. Redox reaction can be defined as the reactions which undergo both oxidations as well as reduction. In other words, one of the elements of reaction undergoes oxidation as well as reduction.
But we will discuss decomposition reactions. Decomposition reactions are the reactions in which there is a breakdown of a compound into two or more components and at least one of them must be in the elemental state.
We will consider one of the examples of decomposition reaction in which carbonic acid $\left( {{H_2}C{O_3}} \right)$ breaks in carbon dioxide $\left( {C{O_2}} \right)$ and water $\left( {{H_2}O} \right)$ which means a single compound breaks in two or more components and one of them is in an elemental state.
The reaction is given ${H_2}C{O_3}\xrightarrow{{}}{H_2}O + C{O_2}$.
Decomposition reactions can be exothermic, endothermic, oxidation, and reduction. But as we know that during the decomposition reactions bond breaks form two or more components.Energy is required to break the bond and energy is released while forming the bonds. Now we will consider option (A) Exothermic. Exothermic reactions are reactions in which energy is released. Option (A) is incorrect.
Option (B) endothermic. Endothermic reactions are the reactions in which energy is absorbed.
Option (C) and (D) are not related to the release or absorption of energy. So we can conclude that most of the decomposition reactions are endothermic.

Therefore, the correct option is (B).

Note:
The most important thing to note is that all decomposition reactions are not redox reactions. For example, the decomposition reaction of calcium carbonate is not a redox reaction.
$CaC{O_3}(s)\xrightarrow{\Delta }CaO(s) + C{O_2}(g)$
There are four types of redox reactions. Combination, displacement, disproportionation, and decomposition reactions.