Solid potassium chloride (KCl) is an ionic compound composed of potassium ions (K+) and chloride ions (Cl-). When considering solubility, it is important to note that ionic compounds tend to dissolve well in polar solvents. Water (H2O) is a highly polar solvent, which means it has a significant difference in electronegativity between its hydrogen and oxygen atoms, leading to a partial positive charge on the hydrogen atoms and a partial negative charge on the oxygen atom. This polarity allows water molecules to surround and interact with the charged ions in KCl, effectively separating them and allowing the compound to dissolve. In contrast, the other options (CH3CH2CH2OH, CH3CH2CH2CH2CH3, and CH4) are either less polar or non-polar, making them less effective at dissolving ionic compounds like KCl.