Electrolysis of heavy water gives deuterium.
\({ 2D }_{ 2 }O\overset { Electrolysis }{ \longrightarrow } { 2D }_{ 2 }+{ O }_{ 2 }\)

(i) By bombarding lithium with slow neutrons
(ii) ₃Li⁶+₀n¹ ➝ ₁T³+₂He⁴

a) Electron-precise hydrides:
These have required number of electron to represent their conventional d lewis structure. All the elements of carbon group (14) form such hydrides.
Eg CH₄, C₂H₆, SiH₄, GeH₄
b) Electron - deficient hydrides:
There act as Lewis acids (ie) electron acceptors. The elements from group (13) form such hydrides.
Eg: B₂H₆
c) Electron - rich hydrides:
There have excess electron, which are present as lone pairs. Elements of group 15-17 form such hydrides. They behave as Lewis bases (ie) electron donors.
Eg: NH₃ ,H₂O, HF

(i) Atomic hydrogen and oxy-hydrogen torches finds use for cutting and welding purposes.
(ii) Atomic hydrogen atoms are allowed to recombine on the surface to be welded to generate temperature of 4000 K.

When conc. H₂SO₄ absorbs H₂O from moist H₂ it produces so much of heat since its highly exothermic and so it may catch fire.

(i) Due to small size of Nitrogen atom.
(ii) Due to polar nature of N-H bond.
(iii) Due to inter molecular H- bonding which are stronger than London forces present in other hydrides. Other hydrides lack H - bonding

Water has higher specific heat, thermal conductivity, surface tension, dipole moment and dielectric constant.
These properties allow water to play a key role in the biosphere.

High dipole moment and high dielectric constant make water as a useful solvent.

High purity hydrogen (> 99.9%) is obtained by the electrolysis of water containing traces of acid or alkali or the electrolysis of aqueous solution of sodium hydroxide or potassium hydroxide using a nickel anode and iron cathode. However, this process is not economical for large-scale production.
 At anode: 2OH^- ➝ H₂O + 1/2O₂ + 2e^-
At cathode: 2H₂O + 2e^- ➝ 2OH^- + H₂
Overall reaction: H₂O ➝ H₂ + 1/2O₂ 

1. Deuterium is used in heavy water moderated fission reactors, usually as liquid D₂O to slow neutrons
2. To prepare D₂O (heavy water)
3. To prepare deuterated halides
4. To prepare compounds like deutero methane, deutero ammonia etc..
5. To manufacture deuterium lamps with quartz or UV glass bulb.

When compounds containing hydrogen are treated with D₂O, hydrogen undergoes an exchange for deuterium
\( 2 \mathrm{NaOH}+\mathrm{D}_{2} \mathrm{O} \rightarrow 2 \mathrm{NaOD}+\mathrm{HOD} \)
\(\mathrm{HCl}+\mathrm{D}_{2} \mathrm{O} \rightarrow \mathrm{DCl}+\mathrm{HOD} \)
\(\mathrm{NH}_{4} \mathrm{Cl}+4 \mathrm{D}_{2} \mathrm{O} \rightarrow \mathrm{ND}_{4} \mathrm{Cl}+4 \mathrm{HOD}\)
These exchange reactions are useful in determining the number of ionic hydrogens present in a given compound.
For example, when D₂O is treated with of hypo-phosphorus acid only one hydrogen atom is exchanged with deuterium. It indicates that, it is a monobasic acid.
\(\mathrm{H}_{3} \mathrm{PO}_{2}+\mathrm{D}_{2} \mathrm{O} \rightarrow \mathrm{H}_{2} \mathrm{DPO}_{2}+\mathrm{HDO}\)

1. Heavy water is widely used as moderator in nuclear reactors as it can lower the energies of fast neutrons
2. It is commonly used as a tracer to study organic reaction mechanisms and mechanism of metabolic reactions
3. It is also used as a coolant in nuclear reactors as it absorbs the heat generated.

Interstitial hydrides have metallic bonding. These are non - stoichiometric; their composition varies with temperature and pressure. The crystal lattice expands due to the inclusion of dihydrogen and there is distortion of crystal lattice. So they have lower density than the parent metal. Recent studies have shown that except the hydrides of Ni, Pd, Ce & Ac, other hydride are different from the parent metals.