Solution:Concept: Both reversible and irreversible alterations have occurred. Reversible change involves a change in the material's shape, size, and physical characteristics. Examples of reversible alterations include paper folding and spring elongation. A piece of wood that has been burned to ash cannot be turned back into the wood. An illustration of irreversible transformation is this.
1) Sodium and water react in this reaction to generate sodium hydroxide while hydrogen is released. The hydrogen gas that has been released is no longer present in the system that is reacting and does not move in the opposite direction. Thus, the reaction cannot be stopped. (1) is the incorrect choice.
2) Silver nitrate and nitric acid combine in this process to produce silver chloride and nitric acid as byproducts. Nitric acid and silver chloride do not react because silver chloride is a stable substance. Thus, the reaction cannot be stopped. (2) is the erroneous choice.
3) In this reaction, sodium chloride and potassium nitrate combine to produce potassium chloride and sodium nitrate as byproducts. Since sodium and potassium both exhibit high reactivity, they can be used to swap out the reactant and product sides. Thus, the reaction can be reversed.
4) Lead nitrate and sodium iodide to combine in this reaction to create precipitates of sodium nitrate and lead iodide. Lead iodide does not react with sodium nitrate because of the precipitation reaction. Thus, the reaction cannot be stopped. As a result, choice (4) is unsatisfactory.
Hence, the correct answer is option 3.