Yes, they are pretty much the same thing. You can either write H30+ or H+ depending on the equation and the type of problem.
Of course it's water (H2O) or hydrogen peroxide (H2O2).
The oxidation state of Hydrogen in the hydronium ion is 1+ and the oxidation state of oxygen is 2-
When acids dissolve in water, they dissociate to form hydronium ions. There is not a substance that's forms truly forms hydrogen ions in water.However, for purposes of convenience the hydronium ions are sometimes referred to as hydrogen ions.
Yes, the hydronium ion (H3O+) is polar due to the uneven distribution of electrons around the molecule. The oxygen atom attracts electrons more strongly than the hydrogen atoms, creating a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms.
Formula of a hydrogen ion is H+, its formula is equal to that of a proton. Also hydrogen may form a hydride anion, H-