The oxidation number of cobalt in \(\mathrm{K}_{3}\left[\mathrm{Co}\left(\mathrm{NO}_{2}\right)_{6}\right]\) is: (a) \(-3\) (b) \(+3\) (c) \(-4\) (d) \(+4\)

Coordination compounds are a class of substances with unique chemical structures consisting of a central metal atom or ion bonded to a group of molecules or anions, termed 'ligands'. These ligands can donate pairs of electrons to the metal, forming coordinate covalent bonds. Such compounds are prevalent in biochemistry and inorganic chemistry and have extensive applications, ranging from catalysis to medicinal chemistry.

In coordination chemistry, it is essential to recognize the charge and coordination number of the central ion, as well as the nature and charge of the ligands, to deduce the overall charge and properties of the compound. The oxidation state of the central metal ion can affect the compound's color, magnetism, and reactivity. An example is the potassium hexanitritocobaltate(III) \(\mathrm{K}_3[\mathrm{Co}(\mathrm{NO}_2)_6]\), where cobalt acts as the central metal ion surrounded by ligands.

Redox chemistry deals with the oxidation and reduction processes whereby atoms undergo changes in their oxidation state through the transfer of electrons. Oxidation pertains to the loss of electrons, while reduction refers to the gain of electrons. This dual nature of redox reactions is pivotal in explaining various chemical phenomena, including the functioning of batteries, corrosion, and metabolic processes in living organisms.

Understanding how to calculate oxidation states is crucial for predicting the outcome of redox reactions. As seen in the exercise, finding the oxidation number involves recognizing that the total charge in a neutral compound sums to zero, and in an ion, it equals the ion's charge. By considering the known oxidation states of certain elements and the overall charge, you can deduce the unknown oxidation state, as done for cobalt in the compound in question.

Importance of Oxidation Numbers in NEET

The National Eligibility cum Entrance Test (NEET) is one of the most significant competitive exams for students aspiring to enter the medical field in India. Chemistry is a substantial part of this examination and understanding concepts like oxidation numbers is essential. Mastering the skill to calculate oxidation numbers not only features in direct questions but also aids in tackling reaction predictions and balancing redox reactions.

Strategy for NEET Chemistry

Preparing for NEET Chemistry involves a systematic study plan covering all the topics thoroughly. Building a strong foundation in core concepts such as coordination compounds and redox chemistry is imperative. Active learning through solving numerous problems, like the one provided, and revisiting challenging concepts frequently can significantly enhance retention and application skills. It's also important to refer to standard textbooks and NEET preparation materials for a focused approach to mastering chemistry and achieving a favorable outcome in the exam.