Solubility and polarity — Which substance will readily dissolve in a polar solvent such as water due to strong ion–dipole interactions?

Introduction / Context:
Solubility is governed by “like dissolves like.” Polar solvents stabilize ions and polar solutes, while nonpolar solvents stabilize nonpolar solutes. Understanding intermolecular forces predicts whether a given solute will dissolve readily.

Given Data / Assumptions:

• Water is a polar solvent with a high dielectric constant.
• Candidate solutes include ionic, nonpolar molecular, and atomic species.
• We are looking for the one that interacts strongly with water.

Concept / Approach:
Ionic compounds like sodium chloride (NaCl) dissociate into Na+ and Cl− in water. Strong ion–dipole interactions between ions and water’s partial charges overcome lattice energy, leading to dissolution. By contrast, nonpolar molecules (methane, gasoline hydrocarbons) and noble gases (argon) lack permanent charges and interact weakly (dispersion forces only), giving low solubility in water.

Step-by-Step Solution:

Verification / Alternative check:
Everyday experience (table salt dissolving quickly) and thermodynamic data (hydration energies) confirm this prediction.

Why Other Options Are Wrong:

• Gasoline (heptanes, octanes): nonpolar, poorly soluble in water.
• Methane: nonpolar gas, very low solubility.
• Argon: monoatomic, nonpolar, weakly soluble via dispersion.

Common Pitfalls:
Assuming small molecules dissolve regardless of polarity; polarity and charge dominate over size in aqueous solubility.

Final Answer:
sodium chloride