* Which equation is NOT balanced?
O 2 Hz + 02 > 2 H20
4 H2 + 2 02 ---> 4H20
H2 + H2 + O2 > H2O + H20
2 H2 + 02 > H20
None of the above

2H₂ + O₂ → H₂O

Explanation:

The unbalanced equation is

          2H₂ + O₂ → H₂O

In a balanced chemical equation, the number of moles of species on both sides of the expression must be the same.

                2H₂ + O₂ → H₂O

                                       Reactant                                 Product

                                      H          O                                   H         O

Number of moles          4           2                                   2           1

We see that the number of hydrogen and oxygen on both sides of the expression differs significantly.

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."