Ack please help on this problem

Only the oxygen needs to be balanced. There are equal numbers of hydrogen and carbon

Explanation:

 Given expression:

     C₂H₄ + O₂ → 2H₂O + 2CO₂

The law of conservation of mass suggests that chemical equations be balanced since atoms are neither created nor destroyed in the course of a chemical reaction. In retrospect, bonds are broken and chemical species are change to another form.

 From the given equation, only oxygen is not balanced. This flouts the law of conservation.

 On the reactant side, we have 2 oxygen on the product, we have 6.

first one is the correct answer

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 !