The right option is; a. a dense ball of solid metal.
Earth’s inner core is a dense ball of solid metal
The earth’s inner core is the most interior (center) part of the earth and it is primarily a dense solid ball that has a radius of about 1,220 km (760 mi). The earth’s inner core is chiefly made up of an iron–nickel alloy (metal) and some other elements and its temperature is about 5400 °C which is the same as that of the surface of the Sun.
