Which one of the following metals will not reduce \(\mathrm{H}_{2} \mathrm{O} ?\) (a) Li (b) \(\mathrm{Fe}\) (c) \(\mathrm{Cu}\) (d) \(\mathrm{Ca}\)

The reactivity series is an empirical arrangement of metals in order of their reactivity from highest to lowest. It is used to predict the outcomes of metal-water reactions as well as other chemical reactions involving metals. In the context of reactivity with water, the series can guide us in understanding why certain metals, like Lithium (Li) and Calcium (Ca), actively react with water, while others, such as Copper (Cu), do not.

For instance, when examining the interaction between metals and water, we find that metals positioned higher in the series will readily react with water to form a metal hydroxide and hydrogen gas. Conversely, metals lower in the series, like Copper (Cu), exhibit minimal to no reaction with water. This is crucial in the field of chemistry, especially when predicting reaction outcomes for experiments or industrial processes.

Displacement reactions are a type of chemical reaction where a more reactive element displaces a less reactive element from its compound. When it comes to metal displacement reactions with water, a metal will displace hydrogen if it is more reactive than hydrogen. As provided in the step-by-step solution, metals like Lithium (Li) and Calcium (Ca), which are high in the reactivity series, can displace hydrogen from water to form hydroxides.

In a displacement reaction, the activity of the metals is key to determining which metal will replace another. To visualize this, consider an aqueous solution containing ions of a less reactive metal; when a more reactive metal is introduced, it takes the place of the less reactive one. Chemistry students preparing for exams like NEET must thoroughly understand displacement reactions, as they are fundamental to predicting and balancing chemical equations in their syllabus.

Preparing for competitive exams like the National Eligibility cum Entrance Test (NEET) demands a strong grasp of core chemistry concepts, including metal reactivity and displacement reactions. For NEET aspirants, understanding the underlying principles that govern the behavior of metals with water is integral because it applies to multiple areas of chemistry, including inorganic chemistry and electrochemistry.

NEET requires students not just to memorize the reactivity series, but also to be able to apply this knowledge to solve problems effectively. They must be proficient in identifying the outcome of reactions, such as which metal can reduce water and which cannot, as showcased in the original exercise. The ability to analyze and reason through these chemical reactions contributes greatly to a student's success in the examination.