How does destructive interference affect the amplitude of a wave?

Waves don't usually reflect when they strike other waves. Instead, they combine. If the amplitudes of two waves have the same sign (either both positive or both negative), they will add together to form a wave with a larger amplitude. This is called constructive interference. If the two amplitudes have opposite signs, they will subtract to form a combined wave with a lower amplitude. This is called destructive interference. Sound waves with higher amplitudes sound louder than sound waves with lower amplitudes. Constructive interference will make a sound louder while destructive interference will make a sound quieter.

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