To determine which graph illustrates the variation of the solubility of a salt in water with an increase in temperature, particularly for an exothermic dissolution process, we need to understand the relationship between temperature, solubility, and the nature of the dissolution process. ### Correct Option: D (IV) #### Explanation of the Correct Answer: 1. **Understanding Exothermic Dissolution**: - An exothermic dissolution process is one where heat is released when a solute (in this case, a salt) dissolves in a solvent (water). This means that the reaction releases energy to the surroundings. - According to Le Chatelier's Principle, if a system at equilibrium is subjected to a change in temperature, the system will adjust to counteract that change. For an exothermic process, increasing the temperature shifts the equilibrium to favor the reactants (in this case, the solid salt), thereby decreasing solubility. 2. **Graphical Representation**: - In a graph where the y-axis represents solubility and the x-axis represents temperature, an exothermic dissolution will show a decrease in solubility as temperature increases. This means that the graph will slope downwards as you move from left to right. 3. **Identifying the Correct Graph**: - The correct graph (D) will show a downward trend, indicating that as the temperature increases, the solubility of the salt decreases. This aligns with our understanding of exothermic dissolution. #### Why the Other Options are Incorrect: - **Option A (I)**: This graph likely shows an upward trend, indicating that solubility increases with temperature. This is characteristic of endothermic processes, where heat is absorbed, not released. Therefore, it cannot represent an exothermic dissolution. - **Option B (II)**: Similar to Option A, this graph may also depict an increase in solubility with temperature. Again, this is not consistent with an exothermic process. - **Option C (III)**: This option might show a flat line or a slight increase in solubility with temperature. While it does not depict a clear downward trend, it does not accurately represent the expected behavior of an exothermic dissolution process. ### Summary of Key Points: - **Exothermic Dissolution**: Heat is released, and increasing temperature decreases solubility. - **Le Chatelier's Principle**: The system shifts to favor the reactants (solid salt) when temperature increases. - **Graph Characteristics**: The correct graph (D) shows a downward slope, indicating decreased solubility with increased temperature. - **Incorrect Options**: A, B, and C depict either an increase or no change in solubility with temperature, which is inconsistent with exothermic dissolution. This understanding is crucial for interpreting solubility trends in relation to temperature changes, especially in the context of exothermic and endothermic processes.