Final answer:
The temperature of the water has the most significant effect on the rate at which salt dissolves in water because it influences the frequency and energy of collisions between solvent molecules and solute particles.
Step-by-step explanation:
The factor that will most affect the rate of dissolving when a student places 15 grams of salt into 225 ml of water is A) The temperature of the water. The temperature affects how quickly the solvent molecules collide with the solute, with higher temperatures leading to a faster dissolution process. This is because heating the solvent increases the kinetic energy of the molecules, leading to more frequent and forceful collisions. On the other hand, the color of the salt, the shape of the container, and the type of salt used do not have a significant effect on the rate of dissolving in comparison to temperature.
Other factors such as the surface area of the solute and agitation (stirring) can also impact the rate of dissolving. A granulated solute has more surface area and will dissolve more quickly than larger pieces. However, for the given options, temperature is the key factor influencing the dissolution rate.