Question

Why is the inner core a solid if it is the hottest layer how is that possible?

Answer 1

There is a lot of pressure on the inner core due to gravity and the amount of mass exerted on the inner core. When there is a lot of pressure, things tend to "mend together" and are solid.

Answer 2

The inner core is solid because it is made of very dense, or heavy, materials - like iron and nickel. Even though it is very hot, these materials don't "melt" very easily, so they stay solid.

Hope this helps! Sorry if it didn't.