Compare and contrast refraction and diffraction

They both can happen to light waves refraction is bending going from one medium to another diffraction is where waves spread out through a hole or interfere through slits

Refraction is when waves, whether physical or electromagnetic, are deflected when the waves go through a substance. The wave generally changes the angle of its general direction...Diffraction is when a wave goes through a small hole and has a flared out geometric shadow of the slit. Diffraction is a characteristic of waves of all types. We can hear around a corner because of the diffraction of sound waves. For instance, if a wall is next to you when you yell, the sound will parallel the wall. The wall may stop, but the voice doesn't; sound will almost turn the corner of the wall. 

The answer is b.the gaseous state is electrically positive, while the plasma state is electrically negative. 

Ithink the answer is c but then again i'm probably wrong