Why is DNA used to show common ancestry ?

while analogous structures show that similar selective pressures can produce similar adaptations (beneficial features). Similarities and differences among biological molecules can be used to determine species' relatedness.

Explanation:

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 !

c is the answer because when something is left after something evaporates that shows the chemical change.