According to the definition of an ideal solution given in the NCERT textbook:

1. Enthalpy of mixing ($\Delta H_{\text{mix}}$): No heat is absorbed or evolved when components are mixed, so $\Delta H_{\text{mix}} = 0$.
2. Volume of mixing ($\Delta V_{\text{mix}}$): The volume of the solution is the sum of the volumes of the components, so $\Delta V_{\text{mix}} = 0$.
3. Pressure change ($\Delta P$): An ideal solution obeys Raoult's Law ($P_{\text{total}} = P_{\text{calculated}}$), so $\Delta P = P_{\text{obs}} - P_{\text{calc}} = 0$.
4. Entropy of mixing ($\Delta S_{\text{mix}}$): Mixing causes an increase in disorder (randomness) of the system. According to the Second Law of Thermodynamics, for any spontaneous process like mixing, the change in entropy is positive. Therefore, $\Delta S_{\text{mix}} > 0$ (non-zero).