Scientists think that the made of liquid iron and nickel, moves to produce earth’s magnetic field.
a. crust
b. mantle
c. outer core
d. inner core

Scientists have collected extensive experimental and observational
data that can be explained by the Earth's inner core being made of
molten iron and nickel, and moving to produce Earth’s magnetic field,
so that scenario is the current prevailing theory.

If you find new evidence that this theory violates, or if you work out
an explanation that explains the existing data better, then the current
theory will be discarded or changed, to fit your new explanation.
That's how science works.

The rearrangement of particles in a physical change. hope this