In water, oxygen is sp³ -hybridised. Due to stronger lone pair-lone pair repulsions than bond pair-bond pair repulsion, the HOH bond angle decreases from 109.5^o to 104.5^o. Thus, water is a bent molecule as shown in figure.

It is a highly polar molecule. Hydrogen peroxide has a non-planar structure. Dipole moment value of H₂O₂ suggests that all the four atoms in H₂O₂ do not lie in a plane. The structure of H₂O₂ in gas phase, can be compared with a book open at angle 111.5^o.The H-O-O bind angle is 94.8^o.

AlCl₃ is a salt of weak base, Al(OH)₃ and a strong acid, HCl. Therefore , in normal water, it undergoes hydrolysis.
\(Alcl_{ 3 }(s)+3H_{ 2 }O(l)\rightarrow Al(OH)_{ 3 }(s)+3H^{ + }(aq)+3Cl^{ - }(aq)\quad \)
Its aqueous solution is acidic in nature. In acidified water, H⁺ ions reacts with Al(OH)₃ to produce Al³ (aq) ions and Al³⁺(aq) and C^-1
(aq) ions.
In alkaline water AlCl₃ yields following products
\(Alcl_{ 3 }(s)+3H_{ 2 }O(l)\rightarrow Al(OH)_{ 3 }(s)+3H^{ + }(aq)+3Cl^{ - }(aq)\)
\(Al\left[ OH \right] ^{ - }_{ 4 }\rightarrow AlO^{ - }_{ 2 }(aq)+2H_{ 2 }O(l)\)
KCl is the salt of a strong acid and a strong base, It does not undergo hydrolysis in normal water. It only dissociates in eater to give K⁺ (aq)+Cl^-(aq)
Aqueous solution of KCl is neutral. Hence, in acidifield water or in alkaline water, the ions do not react further.

Reaction with copper (II) oxide Dihydrogen reduces the copper (II) oxide to metallic copper and itself gets oxidised to water (H₂O).
\({ Cu }_{ 2 }O(s)+{ H }_{ 2 }(g)\rightarrow 2Cu(s)+{ H }_{ 2 }O(l)\)
In Cu₂O the oxidation state of Cu is +2 but in Cu it is present in 0 oxidation state, i.e. dihydrogen reduces Cu from +2 to 0 state.

A major part of all living organisms is made up of water. Human body has about 65% water and some plants have as much as 95% water. It is an essential compound for the survial of all life forms. Iin comparison to other liquids, water has a high specific heat, thermal conductivity, surface tension, dipole moment , dielectric constant etc. These properties allow water to play a key role in biosphere. The high heat of vaporisation and heat capacity are responsible for moderation of the climate any body temprature of living beings. It is an excellent solvent for transportation of minerals and other nutrients for plant and animal metabolism. Water is also required for photosynthesis in plants which releases O₂ into the atmosphere.
\(6CO_{ 2 }(g)+6H_{ 2 }O(l)\xrightarrow [ (hv,chlorophyll) ]{ photosynthesis } C_{ 6 }H_{ 12 }O_{ 6 }+60_{ 2 }\)

Reaction with chlorine when dihydrogen combines with chlorine, it reduces it to the chloride ion (Cl^-) and itself get oxidised to H⁺ ion, to give hydrogen chloride, a covalent compound formed by sharing of a pair of electrons between H and Cl.
\({ H }_{ 2 }(g)+{ Cl }_{ 2 }(g)\rightarrow 2HCl(g)\)