What happens if a test tube containing a solution is left in boiling water for too long?

When a test tube containing a solution is left in boiling water for an extended period, the heat can cause some of the solvent (usually water) to evaporate. This evaporation results in a decrease in the volume of the solution present in the test tube, which leads to a higher concentration of the solute remaining in the solution. Thus, the solubility measurements may be affected because the concentration of the dissolved substances becomes altered due to the loss of water.

Understanding how evaporation interacts with solution concentration is crucial in chemistry, especially when conducting experiments that require precise measurements. If evaporation occurs, it can lead to inaccuracies if one is trying to determine the solubility or the concentration of a solution over time. Hence, option C correctly highlights the impact of prolonged exposure to boiling conditions on the solution's properties.