Which valve is located on an intake and prevents air from entering the pump as the line is charged?

The correct choice for the valve that prevents air from entering the pump as the line is charged is the check valve. A check valve is specifically designed to allow fluid to flow in one direction while preventing backflow, which includes keeping air from entering the system once the pump is operational. This is crucial for maintaining prime and ensuring the efficiency of the pump during operation.

The intake valve is primarily used to control the flow of water into the pump but does not prevent air from entering when the line is charged. The bleeder valve serves a different purpose, generally used to remove trapped air in the system to ensure proper operation, rather than preventing air from entering. The relief valve is designed to relieve excess pressure in the system but does not function in terms of preventing air from being introduced during charging.