b,f,h are already balanced
Answer:

Explanation:
To answer this question successfully, we need to remember that atoms are neutral species, since the number of protons, the positively charged particles, is equal to the number of electrons, the negatively charged particles. That said, we may firstly find an atom which has 3 electrons (and, as a result, 3 protons, as it should be neutral).
The number of protons is equal to the atomic number of an element. We firstly may have an atom with 3 protons and 3 electrons (atomic number of 3, this is Li).
Similarly, we may take the atomic number of 4, beryllium, and remove 1 electron from it. Upon removing an electron, it would become beryllium cation,
.
We may use the same logic going forward and taking the atomic number of 5. This is boron. In this case, we need to remove 2 electrons to have a total of 3 electrons. Removal of 2 electrons would yield a +2-charged cation:
.
We are told we have an oxyacid of the formula HOFO. We will assume the atoms are in this order and will draw a proper lewis structure for this compound by first drawing bonds between each of the 4 atoms and then place the remaining electron pairs on each atom:
.. .. ..
H - O - F - O:
·· ·· ··
We can calculate the formal charge of an atom using the following formula:
Formal charge = [# of valence electrons] - [# of non-bonded electrons + # of bonds]
H: Formal charge = [1]-[0+1] = 0
O: Formal charge = [6]-[4+2] = 0
F: Formal charge = [7]-[4+2] = +1
O: Formal charge = [6]-[6+1] = -1
As we can see the overall charge of the molecule is neutral since the fluorine as a +1 charge and the oxygen a -1 charge.
Mg gained mass because it went from being a single element (on the reactant side) to being a molecule (on the product side).
The the last one, but isn't it c6h12o6?