The correct option is **B. Sodium chloride (NaCl)**. ### Detailed Explanation: 1. **Understanding Polarity and Solubility**: - Solubility in water is largely determined by the polarity of the substance. 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 the Options**: - **A. Octane (C8H18)**: - Octane is a hydrocarbon and is non-polar. It consists of long chains of carbon and hydrogen atoms, which do not have significant charge separation. Because of its non-polar nature, octane does not interact favorably with water molecules and is therefore insoluble in water. - **B. 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 surround the individual 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, making it soluble in water. - **C. Benzene (C6H6)**: - Benzene is a non-polar organic compound. It has a symmetrical structure and does not have significant charge separation. As a result, it does not interact well with water molecules and is insoluble in water. - **D. Iodine (I2)**: - Iodine is a diatomic molecule that is also non-polar. While it can dissolve in some organic solvents, it does not dissolve well in water due to its non-polar nature. The lack of charge separation means that iodine does not interact favorably with polar water molecules. 3. **Why Other Options Are Incorrect**: - **A. Octane (C8H18)**: Non-polar and does not dissolve in polar solvents like water. - **C. Benzene (C6H6)**: Non-polar and does not interact with water, leading to insolubility. - **D. Iodine (I2)**: Non-polar and does not dissolve in water due to lack of interaction with polar molecules. ### Summary of Key Points: - **Polarity**: Water is a polar solvent; polar substances are more likely to dissolve in it. - **Ionic Compounds**: Sodium chloride (NaCl) is ionic and dissociates in water, making it soluble. - **Non-Polar Substances**: Octane, benzene, and iodine 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, which is a common topic in chemistry exams.