Solubility of a substance is its maximum amount that can be dissolved in a specified amount of solvent at a specified temperature. Solubility of a substance depends upon the nature of solute and solvent as well as temperature and pressure. A saturated solution is a solution that is in equilibrium with an excess of solid at a given temperature. A solution that contains a high concentration of solute than does a saturated solution is known as supersaturated solution. If a small crystal of solute is added to a supersaturated solution, the solid will at once crystallize out and an equilibrium will be established. This is known as seeding. More the dielectric constant of a solvent, more is the solubility of polar covalent or ionic compounds in it. Some covalent compounds dissolve in water due to hydrolysis while some other covalent solids dissolve in water due to hydrogen bonding. Ionic compounds dissolve in polar solvents while covalent compounds dissolve in non-polar solvents and this is known as like dissolves like.

The solubilities of ionic compounds often but not always increase with temperature, because energy is required to pull the molecules or ions away from the crystal lattice (lattice energy) \(\Delta H_L\).

Energy is also liberated due to solvation of the solute particles. If the solvent is water, the energy liberated due to solvation is known as hydration energy \(\Delta H_h\).

The energy change when one mole of ionic compound dissolves in water is \(\Delta H_{sol}\).

\[\Delta H_{sol} = \Delta H_h - \Delta H_L\]

Since the hydration energies of the ions and the lattice energy are exothermic changes, they have a negative sign. If \(\Delta H_h\) is more than \(\Delta H_L\), then \(\Delta H_{sol}\) will be negative and the ionic crystal dissolves exothermically.

Iodine is more soluble in alcohol than in carbon tetrachloride because

Dissolution of both is endothermic but heat of dissolution in alcohol is less than in CCl₄

The correct answer is option 4. Dissolution of both is endothermic but heat of dissolution in alcohol is less than in CCl₄.

The solubility of a substance in a solvent depends on several factors, including the polarity of the solvent and solute, as well as the thermodynamics of the dissolution process.

1. Polarity: Polar substances tend to dissolve better in polar solvents, while non-polar substances dissolve better in non-polar solvents. Iodine \((I_2)\) is a non-polar molecule because it consists of two iodine atoms joined by a covalent bond, with no significant difference in electronegativity between the atoms. Carbon tetrachloride \((CCl_4)\) is a non-polar solvent because the carbon-chlorine bonds are highly polar, but they are arranged symmetrically around the central carbon atom, resulting in a net non-polar molecule. On the other hand, alcohol molecules contain a polar hydroxyl \((-OH)\) group, giving them some degree of polarity. Although alcohols are not as polar as water, they still have more polar character than carbon tetrachloride. Therefore, iodine is more soluble in alcohol due to the presence of polar groups in alcohol molecules.

2. Thermodynamics of Dissolution: The dissolution of a solute in a solvent involves breaking intermolecular forces in the solute and solvent and forming new solute-solvent interactions. This process can either release heat (exothermic) or absorb heat (endothermic). In the case of iodine, its dissolution in alcohol is typically exothermic, meaning it releases heat to the surroundings. This indicates that the solute-solvent interactions between iodine and alcohol are energetically favorable. Conversely, the dissolution of iodine in carbon tetrachloride is less exothermic or even endothermic, meaning it absorbs heat from the surroundings. This suggests that the solute-solvent interactions between iodine and carbon tetrachloride are less favorable thermodynamically. The difference in the energy change during dissolution affects the solubility of iodine in the two solvents.

In summary, iodine is more soluble in alcohol than in carbon tetrachloride because alcohol has some degree of polarity, and the dissolution process in alcohol is typically exothermic, favoring the formation of iodine-alcohol interactions.