Whose experiments on the quasi-optical properties of very short radio waves led him to make improvements on the coherer, an early form of radio detector?

Jagadish Chandra Bose

The correct answer is Option (2) → Jagadish Chandra Bose

Jagadish Chandra Bose conducted pioneering experiments on the quasi-optical properties of very short radio waves (microwaves) and, based on this work, made significant improvements to the coherer, which was an early radio-wave detector.