Final answer:
The dependent variable in John's experiment on the effect of temperature on dissolving sugar in water is the time taken for sugar to dissolve.
Step-by-step explanation:
John wants to investigate the effect of temperature on dissolving sugar in water. His dependent variable is the time taken for sugar to dissolve. This is because the dependent variable is the outcome that is measured in the experiment, which, in this case, is how long it takes for sugar to dissolve at different temperatures. Temperature is the independent variable because it is what John is changing to observe how it affects the dissolution rate. The dissolution of sucrose in water serves as a classic example in chemistry of how solubility and dissolution rates are influenced by temperature, among other factors such as agitation, surface area of the solute, and saturation levels.