If anyone could explain which block in the periodic table has metals with changing oxidation numbers and why, it would be greatly appreciated

D-block

Explanation:

Transition metals are metals of the d-block elements located between group 2 and 3 in the periodic table. They are called d-block element because the filling of electrons in their electronic configuration ends in the d-orbital.

Now, they have variable oxidation state because of their partially filled 3d orbital i.e the 3d orbital is not completely filled.

if you mean hydrogen and oxygen then water is the product