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Which of these types of chemical reactions is NOT a redox reaction?
A.Decomposition into elements
B.Single replacement
C.Double replacement
D.Combustion
E.Synthesis of two elements

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Last updated date: 22nd Feb 2024
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IVSAT 2024
Answer
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Hint: An oxidation-reduction (redox) reaction is a type of chemical reaction that involves a transfer of electrons between two species. An oxidation-reduction reaction is any chemical reaction in which the oxidation number of a molecule, atom, or ion change by gaining or losing an electron.

Complete Step-by-Step Answer:
Before we move forward with the solution of the given question, let us first understand some basic important concepts.
1.Decomposition reactions involve the formation of new products by decomposing or breaking a given compound. To put it in simpler terms, decomposition reactions form many products from one reactant in the same reaction. Usually, the oxidation states in the elemental form is zero, and the elements have their certain oxidation states in the compound. When decomposition into elements takes place, the oxidation number of one constituent increases from a negative value to zero, while the oxidation state of the other atoms decreases from a positive value to zero. Hence, decomposition into elements is a redox reaction.
e.g. \[2{H_2}O \to 2{H_2} + {O_2}\]
2.Single replacement reaction occurs when one element in the elemental state, replaces another element in a compound. These reactions are redox reactions because two different elements exist as free elements or exist in their elemental state (oxidation number is zero) on either side of the chemical equation. Hence, there is a change in their oxidation states.
e.g.
\[Zn + 2HCl \to ZnC{l_2} + {H_2}\]
3.Double replacement reaction involves the replacement of one element from one compound, by another element from the other compound. In simpler terms, we can say that these reactions involve only recombination of ions without the actual transfer of electrons. Hence, there is no change in the oxidation states of the elements. Hence, double replacement reactions are not redox.
e.g. \[N{a_2}S{O_4} + Ba{(N{O_3})_2} \to 2NaN{O_3} + BaS{O_4}\]
4.Combustion reactions also involve shifting in the values of oxidation states because elements are usually transferred compounds in this case. Oxygen, which is used in the oxidation state of zero, gets transformed into another oxidation state when it combines with the compound. This also causes a shift in the oxidation value of the elements in the elements in the compound. Hence, combustion reactions are redox reactions
e.g. \[2{C_8}{H_{18}} + 25{O_2} \to 16C{O_2} + 18{H_2}O\]
5.Synthesis of two elements is a reaction in which two or more substances combine to form a more complex product. These reactions are redox reactions.
e.g. \[2Cl + {H_2} \to 2HCl\]
Hence, Option C is the correct option

Note: The ion or molecule that accepts electrons is called the oxidizing agent; by accepting electrons it causes the oxidation of another species. Conversely, the species that donates electrons is called the reducing agent.