What is \(\mathrm{X}\) in the following reaction? \(\mathrm{KHSO}_{4}+\mathrm{F}_{2} \rightarrow \mathrm{HF}+\mathrm{X}\) (a) \(\mathrm{K}_{2} \mathrm{SO}_{4}\) (b) \(\mathrm{K}_{2} \mathrm{~S}_{2} \mathrm{O}_{4}\) (c) \(\mathrm{K}_{2} \mathrm{~S}_{2} \mathrm{O}_{2}\) (d) \(\mathrm{K}_{2} \mathrm{~S}_{2} \mathrm{O}_{8}\)

In chemistry, a single displacement reaction, also known as a substitution reaction, involves the replacement of one element in a compound by another more reactive element. This type of reaction is represented by the general equation A + BC → AC + B, where element A displaces element B in compound BC to form a new compound AC and releases the displaced element B.

For example, in the reaction given in the exercise, \( \mathrm{F}_2 \) is the more reactive element that displaces the hydrogen in \( \mathrm{KHSO}_4 \) to produce hydrogen fluoride (HF) and a new compound X. One key characteristic of such reactions is the reactivity series of metals, which can help predict which metals will displace others based on their reactivity. For nonmetals like halogens, the trend in reactivity decreases as you go down the group in the periodic table. Therefore, fluorine, as the most reactive halogen, can displace other halogens from their compounds.

Oxidation states, also referred to as oxidation numbers, are a conceptual charge that an atom would have if all its bonds were ionic with no covalent component. They are essential for understanding the transfer of electrons in redox reactions and are useful for balancing chemical equations.

Determining the oxidation state of an atom within a compound involves a few rules:

• The oxidation state of a free element is always zero.
• For monoatomic ions, the oxidation state is equal to the charge of the ion.
• Oxygen typically has an oxidation state of -2, except in peroxides or when bonded to fluorine.
• Hydrogen usually has an oxidation state of +1 when bonded to nonmetals, and -1 when bonded to metals.
• The sum of oxidation states in a neutral compound must be zero, while in a polyatomic ion, it must be equal to the ion's charge.

In the given exercise, we observe that the sulfate ion (\( \mathrm{SO}_4^{2-} \)) maintains its structure and oxidation states throughout the reaction. Therefore, potassium must balance the charge in the resulting salt, which helps in identifying the correct product X.

The National Eligibility cum Entrance Test (NEET) is a highly competitive exam in India for students aspiring to enter medical courses. Chemistry is one of the core subjects of the NEET syllabus and requires rigorous preparation. Students need a firm grasp of various topics, including atomic structure, chemical bonding, stoichiometry, thermodynamics, and chemical kinetics.

To prepare effectively for NEET chemistry, it's important to:

• Understand the basic concepts and principles thoroughly.
• Practice solving various types of chemical reactions, including single displacement reactions, which are common in NEET exams.
• Get comfortable with determining oxidation states as they're crucial for balancing chemical equations and redox reactions.
• Familiarize oneself with the periodic table trends and chemical properties of elements.
• Use NEET-specific study materials and past year question papers to acclimate to the exam pattern and time constraints.

Concepts like single displacement reactions and oxidation states form the foundation for advanced topics in chemistry, and their application is often tested in exams like NEET. Through consistent practice and understanding of these concepts, students can enhance their problem-solving skills and improve their chances of performing well in competitive exams like NEET.