### Correct Option: A. Sodium chloride (NaCl) #### Detailed Explanation: 1. **Understanding Polarity and Solubility**: - Solubility in water is largely determined by the polarity of the substances involved. Water is a polar solvent, meaning it has a partial positive charge on one side (the hydrogen atoms) and a partial negative charge on the other side (the oxygen atom). Polar substances tend to dissolve well in polar solvents due to the "like dissolves like" principle. 2. **Analyzing Sodium Chloride (NaCl)**: - Sodium chloride is an ionic compound composed of sodium ions (Na⁺) and chloride ions (Cl⁻). When NaCl is added to water, the polar water molecules interact with the charged ions. The positive end of water molecules (hydrogens) is attracted to the negatively charged chloride ions, while the negative end (oxygen) is attracted to the positively charged sodium ions. This interaction leads to the dissociation of NaCl into its constituent ions, allowing it to dissolve in water. 3. **Examining the Other Options**: - **B. Octane (C8H18)**: - Octane is a hydrocarbon and is non-polar. Non-polar substances do not interact favorably with polar solvents like water. Instead, they tend to separate from water, leading to poor solubility. Therefore, octane is not soluble in water. - **C. Iodine (I2)**: - Iodine is a non-polar molecule. Although it can dissolve in some organic solvents, it does not dissolve well in water due to its non-polar nature. The lack of significant interaction between iodine molecules and water molecules results in low solubility. - **D. Benzene (C6H6)**: - Benzene is also a non-polar molecule. Similar to octane and iodine, benzene does not interact well with water. Its non-polar characteristics prevent it from dissolving in polar solvents like water. 4. **Conclusion**: - Among the options provided, sodium chloride (NaCl) is the only substance that is ionic and polar, making it highly soluble in water. The other substances (octane, iodine, and benzene) are non-polar and do not dissolve in water. #### Summary of Key Points: - **Polarity**: Water is a polar solvent; polar substances dissolve well in it. - **Ionic Compounds**: Sodium chloride (NaCl) dissociates into ions in water, leading to high solubility. - **Non-Polar Substances**: Octane, iodine, and benzene are non-polar and do not dissolve in water. - **"Like Dissolves Like" Principle**: Polar substances dissolve in polar solvents, while non-polar substances do not. This understanding of solubility based on polarity is crucial for predicting how different substances will behave in aqueous solutions.