(i) An ideal solution which obeys Raoult's law over entire range of concentration. The necessary condition to reach ideal solution is:Enthalpy of mixing of the pure components to form the solution, $\Delta H_{\text{mix}} = 0$ and volume of mixing, $\Delta V_{\text{mix}} = 0$(ii) Molarity is defined as the number of moles of solute present in $1000\ \mathrm{mL}$ of the solution. Molarity is represented by $M$.$M = \frac{\text{Number of moles of solute}}{\text{Volume of solution in mL}} \times 1000$