What is applied to electrodes located in the water of a storage tank?

The correct choice is based on the principles of cathodic protection, which is commonly used to prevent corrosion in water storage tanks. Cathodic protection systems often utilize direct current (DC) applied to electrodes submerged in the water. This method helps to protect the metal surfaces of the tank from rust and deterioration by driving the corrosive reactions in the opposite direction.

In contrast to AC current, which alternates and is not typically effective in providing protective current for corrosion control, DC current maintains a consistent flow that is crucial in electrochemical processes. A digital signal is not applicable in this scenario as it relates more to data transmission and control rather than corrosion prevention. Similarly, static charge refers to an imbalance of electric charge on an object, which does not play a role in the protection of storage tank materials.

Thus, DC current is the proper solution for applying to electrodes in the water of a storage tank, ensuring the effectiveness of the corrosion prevention strategy.