How have scientists been able to determine the composition of earth's layers? A. by looking at how X-rays affect the planet
B. by studying the magnetic fields of various planets and moons
C. by looking at how seismic waves change speeds as they travel through Earth
D. by studying layers of other planets and moons

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !