Here are the correct matches between Column A and Column B:
1. **Concentration** - **a.** The amount of one substance in a certain volume of another substance.
2. **Saturated Solutions** - **b.** A solution with as much dissolved solute as it can hold at a given temperature. No more solute can be dissolved.
3. **Unsaturated Solution** - **d.** A solution that holds less solute than is possible at a given temperature. More solute can dissolve.
4. **Supersaturated Solution** - **c.** A heated solution that holds more dissolved solute than is possible at a lower temperature.