Which of the following tools is essential for aligning railway tracks?

The essential tool for aligning railway tracks is a track gauge. A track gauge is specifically designed to measure and ensure the correct distance between the rails, known as the gauge distance. This measurement is critical for safe and efficient train operations, as even small deviations can lead to derailments or other safety issues.

Using a track gauge allows mechanics and workers to maintain the proper spacing between the tracks throughout various segments of track installation or repair. This alignment is necessary for trains to operate smoothly and safely, as tracks that are not adequately aligned can cause problems in the movement of trains.

The other tools listed have different functions. A mallet is typically used for driving spikes or setting track components, but it does not measure alignment. A level is useful for ensuring a flat surface in general construction, while a pry bar assists with lifting and moving heavy objects or adjusting position, but neither of these tools serves the specific purpose of measuring and aligning the track gauge distance. Therefore, the track gauge is the only tool that precisely fulfills the role required for aligning railway tracks.