The radius of Earth's inner core is roughly 1,220km (658miles), made of mostly (about 80%) solid iorn.
Solid
I know it is nickel
Because the outercore applies pressure to the innercore. Its like the book stack effect, pile up 5 books. Which book has the most pressure on it? The bottom. Now imagine that being a CIRCLE of books, the INNERbook or the innercore would have the most pressure.
crust mantle outtercore innercore
hot burning rock and magma
lithosphere asthenospere mesosphere outercore innercore
Around 5,400 degrees Celsius to 6,000 degrees Celsius.
Heavy (or dense) ones ...mostly iron.
inner core
The centre of the Earth's core - is a solid iron sphere.
Earth's inner core is farther from the surface than its outer core. The molten liquid outer core extends from about 1,800 to 3,200 miles below Earth's surface, and the solid inner core extends from about 3,200 miles to the center of Earth, at a depth of about 4,000 miles.
The Wikipedia article on "Earth" mentions that at the center, the temperature "may" be up to 6000 degrees Celsius.