Final answer:
The question pertains to the fact that synthesis and decomposition reactions in chemistry are inherently non-neutral concerning energy. Synthesis reactions absorb energy and are endothermic, while decomposition reactions release energy and are exothermic. An exchange reaction simultaneously incorporates both aspects, with energy being both consumed and emitted.
Step-by-step explanation:
In the realm of chemistry, reactions are categorized based on the changes they induce upon reactants to form products. A synthesis reaction combines multiple reactants into a single product, which often requires an input of energy. Conversely, in a decomposition reaction, a singular compound breaks apart to form multiple products, which typically results in the release of energy.
The nature of these reactions in terms of energy makes them non-neutral; synthesis reactions are endothermic (absorb energy), while decomposition reactions are exothermic (release energy). However, an exchange reaction is an interesting case where both synthesis and decomposition can occur simultaneously, involving the breaking and forming of bonds, and the exchange of energy.
For instance, in the given example c. (NH4)2Cr2O7 → Cr2O3 +4H2O + N2, we can identify that this is a decomposition reaction because a single compound breaks down into multiple products. This contrasts with a synthesis reaction that would take the form A + B → AB, merging two reactants into one product.