Fluorine ion by a process of hydrogen bonding forms the anion [HF₂]^-. Hence, in the presence of an alkali like KOH, HF forms salt-like compounds like KHF₂.

Complex- Addition compounds which do not give all their constituent ions when dissolved in water, individual identity of ions are lost,
eg,- [Cu(NH₃)₄]SO₄, LiAIH₄.

Lewis acid- Electron deficient species which gain electrons while forming a bond with Lewis bases. eg,-B₂H₆.
Interstitial metal hydrides- f-block hydrides are non-stoichiometric eg, LaH_n, etc, where chemical composition is variable eg,- LaH_2.87, X_bH_2.5 etc.
Intermediate hydride- Polymeric in nature eg, BeH₂
Covalent hydride- Bond forms by sharing of electron. eg, AsH₃.

For the laboratory preparation of H₂O₂, BaO₂ is added to ice cold solution of sulphuric acid.
BaO₂ + H₂SO₄ →  BaSO₄ + H₂O₂

H₂O₂ can be prepared by electrolysis of 50% H₂SO₄. In this method, hydrogen is liberated at cathode.

Electrolysis of a hydrochloric acid solution produces oxygen at anode and hydrogen at cathode.
The products of electrolysis of dilute solutions of all acids are same as the products of electrolysis of water.

Sublimation is not used for concentration of hydrogen peroxide. H₂O₂ does not sublime, it decomposes at a temperature below its boiling point.

To very dilute hydrogen peroxide is added a dilute solution of potassium dichromate acidified with sulphuric acid. The solution is rapidly shaken with ether, which floats to the surface with a beautiful blue colour. An unstable perchromic acid is formed, which dissolves in ether to form a blue liquid.

O₂F₂ molecule resembles H₂O₂ in structure.

When hydrogen peroxide is added to an acidified solution of potassium dichromate (or any other Cr (VI) species), a very complicated reaction occurs. The product depends on the pH and the concentration of Cr (VI) ion.
Cr₂O₇^2- + 2H⁺ + 4H₂O₂ → 2CrO(O₂)₂ + 5H₂O
A deep blue-violet coloured peroxo compound is formed.
Thereafter the solution turns olive green as CrO₅ decomposes to form Cr₂O₃.

Reaction of impure Zn with dil. HCl is not used for commercial production of dihydrogen due to low yield.