An additive used to reduce water surface tension and hose friction is:

The correct answer is dish soap because it contains surfactants, which are substances that lower the surface tension of water. When added to water, these surfactants help to break up the cohesive forces between water molecules, allowing the water to spread more effectively and penetrate materials more readily. This property is particularly useful in firefighting, as it can enhance the effectiveness of water in extinguishing fires by increasing its ability to reach the burning materials and improve the overall flow of water through hoses, reducing friction.

Unlike the other options, dish soap is specifically designed to manipulate surface tension. Water softeners primarily target minerals in water rather than changing surface tension. Grease and oil may create a slippery surface but do not help in reducing water’s surface tension and can actually complicate firefighting efforts by creating additional hazards. Therefore, dish soap is the most appropriate choice for this context.