Question. Context: The Earth's inner core is the Earth's innermost part. It is primarily a solid ball with a radius of about 1,220 kilometres (760 miles), which is about 70 % of the Moon's radius. It is composed of an iron -- nickel alloy and some light elements. The temperature at the inner core boundary is approximately 5700 K (5400 ° C).

Question: composition of the inner core of the earth?
Answer. an iron -- nickel alloy and some light elements
What step-by-step reasoning justifies that answer?
Reasoning: The relevant information to answer the above question is: It is composed of an iron -- nickel alloy and some light elements.