Which of the following does not represent redox reactions? (a) \(\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+2 \mathrm{OH}^{-} \longrightarrow \mathrm{CrO}_{4}^{2-}+\mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{SO}_{5}^{2-}+2 \mathrm{I}^{-}+2 \mathrm{H}^{+} \longrightarrow \mathrm{I}_{2}+\mathrm{SO}_{4}^{2-}+\mathrm{H}_{2} \mathrm{O}\) (c) \(2 \mathrm{Ca}(\mathrm{OH})_{2}+2 \mathrm{Cl}_{2} \longrightarrow \mathrm{Ca}(\mathrm{ClO})_{2}+\mathrm{CaCl}_{2}+\) \(2 \mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{PCl}_{5} \longrightarrow \mathrm{PCl}_{3}+\mathrm{Cl}_{2}\)

Oxidation states are an essential aspect of understanding redox reactions in chemistry. They serve as a tool to track how electrons are transferred between atoms. In a redox (reduction-oxidation) process, one atom's oxidation state increases, indicating it has lost electrons, while another's decreases, showing a gain of electrons.

For example, the oxidation state of each element is determined considering known values—like the typically -2 state for oxygen—and overall charge balance within the molecule. Knowing oxidation states is crucial when identifying redox reactions. A reaction lacking such changes, as in option (a), is not redox, highlighting the absence of electron transfer among participating atoms. In steps 1 through 4 of the exercise, systematic analysis of oxidation states reveals which substances undergo change. Through valence changes of chromium, sulfur, chlorine, and phosphorus, students can deduce the redox nature of the reactions, with (a) being the exception. For NEET chemistry preparation, a solid grasp of assigning oxidation numbers is invaluable for solving complex problems and theoretical questions related to redox chemistry.

Chemical reactions are the heart of chemistry, where reactants transform into products through the making and breaking of chemical bonds. Redox reactions are a significant category among various types of chemical processes. They are characterized by an exchange of electrons, leading to changes in oxidation states, as seen in the textbook exercise.

In every chemical reaction, conservation principles are at play, such as the conservation of mass, charge, and energy. Understanding how to balance equations, like in the given exercise, is essential for maintaining these conservation laws. For students, developing the skill to categorize and balance different reactions, such as synthesis, decomposition, single replacement, and double replacement—alongside redox reactions—will be pivotal throughout their chemistry education, especially for competitive exams like NEET, where they are tested on both conceptual understanding and practical applications.

Preparing for NEET (National Eligibility cum Entrance Test) requires a focused approach, especially in chemistry, which is divided into physical, organic, and inorganic branches. Redox reactions feature prominently within physical and inorganic chemistry. A comprehensive preparation plan should include a strong foundation in concepts like oxidation states and chemical reaction mechanisms.

To excel, students should deepen their understanding through exercises such as the one provided, which hones their ability to identify and analyze redox reactions. Regular practice in determining oxidation states, balancing complex reactions, and understanding electron exchange will significantly enhance their aptitude for the NEET examination. High-quality resources, consistent problem-solving, and conceptual clarity are key strategies to succeed in one of the most challenging competitive exams for aspiring medical students in India.