The correct answer is option 4. obey Raoult's law.
- \(\Delta H_{mix} \neq 0\): This statement means the enthalpy of mixing for a non-ideal solution is not zero. When solute and solvent molecules interact differently than in their pure states, energy can be released (negative ΔHmix) or absorbed (positive ΔHmix) during mixing, leading to a non-zero value.
- \(\Delta _{mix} \neq 0\): This statement means the volume of mixing for a non-ideal solution is not zero. The combined volume of the solute and solvent after mixing might not be equal to the sum of their individual volumes due to changes in intermolecular interactions and packing arrangements.
- Do not obey Raoult's law: This statement is true because non-ideal solutions deviate from Raoult's law, which assumes ideal interactions between solute and solvent molecules. Their vapour pressure will either be higher (positive deviation) or lower (negative deviation) than predicted by Raoult's law based on the nature of the interactions.
- Obey Raoult's law: This statement is not true for non-ideal solutions. As mentioned above, the very definition of a non-ideal solution implies it does not strictly follow Raoult's law due to non-ideal interactions between solute and solvent molecules.
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