A water molecule is made up of one oxygen and two hydrogen atoms. Why is water considered a pure substance? - Water can be combined with other substances by physical means.
- Water molecules are made up of different types of atoms.
- Water can not be broken down by physical means.
- Each water molecule has an identical composition and properties.

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 !

a polar bond is formed when electrons are shared unevenly between atoms

you need to have a picture of the atom that way we can answer it