Final answer:
The inner core is solid metal due to high temperature and pressure, while the outer core is molten metal due to slightly lower pressure.
Step-by-step explanation:
The Earth's core is composed of two parts: the inner core and the outer core. The inner core is solid and mainly consists of metals such as iron, nickel, and sulfur. The temperature in the inner core is extremely high, reaching around 2,500°C. On the other hand, the outer core is molten metal due to its slightly lower temperature.
The reason for the difference in state between the two cores is mainly due to the pressure. The inner core is under higher pressure compared to the outer core. The immense pressure in the inner core is strong enough to keep the metals in a solid state despite the high temperature. In the outer core, however, the pressure is slightly lower, which allows the metals to melt and behave as a liquid.