Which type of fuel quantity indicating system utilizes a bridge circuit for operation?

The electronic fuel quantity indicating system utilizes a bridge circuit for its operation, making it the correct choice. This system typically employs a resistor bridge circuit that allows for precise measurement of fuel levels through electrical resistance changes. When the fuel level varies, the resistance in the circuit changes, and this variation is used to determine the quantity of fuel present.

Bridge circuits are particularly effective in electronic systems because they can provide accurate readings and are less prone to errors that might affect mechanical or pneumatic systems, which operate based on physical movement or pressure changes, and not on direct electrical measurements.

In mechanical systems, fuel quantity is often indicated by moving parts, such as floats or gauges, which do not rely on electronic bridge circuits. Pneumatic systems operate using air pressure changes to gauge levels, while optical systems use light sensors to detect liquid levels, neither of which involves a bridge circuit. Thus, the electronic system stands out as the only one among the options that functions based on the principles of a bridge circuit.