Sound consists of a wave of vibrations of particles so it must have a material substance to pass through. So sound can pass through solids, liquids and gases but not through a vacuum. See http://www.school-for-champions.com/science/sound.htm
Sound travels through mediums in sound waves.
in stiff and not stiff mediums stiff mediums are too strong to let the sound wave molecules pass through, whereas less stiff mediums eventually leave the sound waves to loose energy as they pass through. the atmosphere would have to be just right from mediums, no more, no less.
If by best you mean fastest and/or furthest, than sound travels better through liquid. This is because the speed (and distance) of sound is dependent on the density of the medium it is traveling through. Since sound waves travel better with compression, they move faster in more solid mediums because of the mediums' tightly packed molecules.
For most mediums, a higher temperature results in higher density, and sound travels through denser mediums faster than through less dense mediums, so a lower temperature generally increases the speed of sound waves.
For most mediums, a higher temperature results in higher density, and sound travels through denser mediums faster than through less dense mediums, so a lower temperature generally increases the speed of sound waves.
Air, water, solid.
Metals such as iron
Yes, sound can change its medium.
Yes, sound can travel through most mediums effectively, as long as the amplitude and frequency of the sound wave is great enough.
Sound can penetrate those mediums.
because of material density
Yes, sound can travel through most mediums including solids and liquids. However, it cannot travel through a vacuum.