Answer:

1) By looking at the seismic waves from earthquakes.

2) There are two types of waves these are the S wave and the P wave.S waves cannot pass through the liquid outer core, but P waves can.Because the waves are refracted as they travel through the Earth due to a change in density of the medium.

3) The temperature of the inner core is far above the melting point of iron.However, unlike the outer core, the inner core is not liquid or even molten.The liquid outer core separates the inner core from the rest of the Earth, and as a result, the inner core rotates a little differently than the rest of the planet.