When microwave signals follow the curvature of earth, this is known as ducting.

Correct Option: B

When microwave signals follow the curvature of earth, this is known as ducting.

Diffraction of electromagnetic waves may occur around the edge of a sharp obstacle.

Correct Option: D

Diffraction of electromagnetic waves may occur around the edge of a sharp obstacle.

Electromagnetic waves are refracted when they pass into a medium of different dielectric constant.

Correct Option: A

Electromagnetic waves are refracted when they pass into a medium of different dielectric constant.

The absorption of radio waves by the atmosphere depends on their frequency.

Correct Option: A

The absorption of radio waves by the atmosphere depends on their frequency.

As electromagnetic waves travel in free space, only attenuation can happen to them.

Correct Option: B

As electromagnetic waves travel in free space, only attenuation can happen to them.