Which layer is a solid made mostly of nickel and iron? a) crust b) astenosphere c) inner core d) none of the above

C. The inner core is known to be made mostly of nickel and iron. However, since there is an outer core (which is the original one that's made out of nickel and iron), your answer might be D. But if you put it the 'core' in general, the right answer should be C.

Magma forms by partial melting of upper mantle and crust. partial melt means that only a fraction of the available material forms a melt, and that the remainder stays solid. the partial melt rises because of its lower density and ascends through he crust. this is so conclusive mean the answer would be magma igneous rocks or balistic magma.