Which one of the following instruments is used for locating submerged objects in an ocean?

Detailed Solution:

The correct answer is “SONAR”.

SONAR (Sound Navigation and Ranging) is specifically designed to detect and locate objects underwater by emitting sound waves and interpreting the echoes that return.

Audiometer: Measures hearing ability.  
Galvanometer: Detects and measures small electric currents.  
Sextant: Used for measuring angles, primarily for navigation.