Which of the following is used to cool and lubricate the lens/grinding wheel interface during grinding?

The correct answer is coolant. Coolants are specifically formulated fluids used during the grinding process to maintain optimal temperatures and reduce friction between the lens material and the grinding wheel. They help to dissipate heat generated from the grinding action, which can lead to thermal damage to both the lens and the grinding wheel if not managed properly. Additionally, coolant serves to lubricate the interface, preventing wear and extending the life of the grinding equipment.

Water, while it can be used in some instances, may not provide the necessary lubrication or cooling properties that a dedicated coolant would. Oil, on the other hand, is generally not used in this context due to its potential to create a buildup of residue on equipment, which can interfere with the grinding process. Solvents are typically employed for cleaning or preparing surfaces, but they do not serve the specific cooling and lubricating functions required during grinding operations.