To determine the quantity that changes with temperature, we examine the definitions and properties of mole fraction, mass percentage, molarity, and molality.
Mole Fraction: The ratio of a component's moles to the total moles in the mixture. This dimensionless quantity is temperature-independent.
Mass Percentage: The mass of a component relative to the total mass of the mixture, expressed as a percentage. As mass is unaffected by temperature, this quantity remains constant.
Molarity (M): Defined as moles of solute per liter of solution. The formula is \(M = \frac{n}{V}\), where \(n\) is moles and \(V\) is solution volume in liters. Since solution volume changes with temperature due to thermal expansion/contraction, molarity is temperature-dependent.
Molality (m): Defined as moles of solute per kilogram of solvent. The formula is \(m = \frac{n}{m_{\text{solvent}}}\). Because the mass of the solvent does not change with temperature, molality is temperature-independent.
Consequently, Molarity is the only quantity among the options that varies with temperature due to its dependence on the solution's volume.
Therefore, the correct answer is Molarity.
Exam Tip: Quantities dependent on volume (e.g., molarity) are temperature-dependent, while those dependent on mass (e.g., mass percentage, molality) are not.
