In July 2018, a stable body of liquid water was found on Mars using a radar instrument on board the European Space Agency's Mars Express orbiter. The tool that was used for the discovery is called:

MARSIS

The correct answer is Option (1) → MARSIS

The tool that was used for the discovery of a stable body of liquid water on Mars in July 2018 is called the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS), which is a radar instrument on board the European Space Agency's Mars Express orbiter.