Which of the following observations best indicates that a solution is supersaturated?

• A. The temperature of the solution decreases rapidly upon stirring.
• B. The solution remains clear and no solid forms even after adding more solute.
• C. Crystals form spontaneously when a small seed crystal is added.
• D. The solution conducts electricity better than a saturated solution.

Answer: (C)

Verified step by step guidance

1. Understand the concept of saturation in solutions: A saturated solution contains the maximum amount of solute dissolved at a given temperature, while an unsaturated solution can dissolve more solute, and a supersaturated solution contains more dissolved solute than the saturation point under normal conditions.
2. Recognize that a supersaturated solution is unstable and can precipitate excess solute if disturbed, such as by adding a seed crystal, which provides a surface for crystallization to begin.
3. Analyze each observation: a rapid temperature decrease upon stirring is not a typical indicator of supersaturation; a solution remaining clear after adding more solute suggests it is unsaturated or saturated but not supersaturated; improved electrical conductivity relates to ion concentration, not supersaturation.
4. Identify that the key sign of supersaturation is the spontaneous formation of crystals when a seed crystal is introduced, as this triggers the excess solute to come out of solution.
5. Conclude that the observation 'Crystals form spontaneously when a small seed crystal is added' best indicates a supersaturated solution because it demonstrates the solution contains more solute than it can normally hold and is ready to precipitate under the right conditions.