What property of a pesticide increases its likelihood to move with water and surface runoff?

The likelihood of a pesticide moving with water and surface runoff is significantly influenced by its solubility in water. When a pesticide has high solubility, it means that it can easily dissolve in water, allowing it to be transported with water flow. This solubility increases the potential for the pesticide to enter waterways through runoff, especially during rainfall or irrigation events.

In contrast, other properties such as viscosity, volatility, and toxicity do not directly affect the movement of pesticides with water runoff. High viscosity could impede movement, while high volatility pertains to a substance's tendency to evaporate rather than be carried by water. High toxicity refers to the harmful effects of a substance but does not relate to its mobility in water. Therefore, high solubility is the critical factor that enhances a pesticide’s tendency to move with water, making it the correct answer.