Answer !
the big bang theory predicted

choose one or more:
a. hubble's law.
b. the cosmological principle.
c. the abundance of helium.
d. the period-luminosity relation of cepheid variables.
e. the cosmic microwave background radiation.
f. that the sky should be dark at night.

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 !

the answer is c.the valence of the atoms combine .