Since s-electrons are closer to the nucleus, therefore as the s-character of the orbital making the C-H bond increases the electrons of C-H bond lies closer and closer to the carbon atom. In other words, the partial +ve charge on the H-atom and hence the acidic character increases as the s-character of the orbital increases. Thus, the acidic character decreases in the order: Ethyne > Benzene> Hexane.

(i) In aryl halides, the strong -/ effect of the halogens decreases the electron density of benzene ring, thereby deactivating it for electrophilic attack.
(ii) The presence of lone pair on halogens is involved in resonance with n-electrons of the benzene ring and it increases the electron density at ortho and para position. Hence the halogen group is an ortho-para director and a deactivator.

(i) BHC is Benzene hexachloride.
(ii) Benzene reacts with three molecule of Cl₂ in the presence of sunlight or UV light to yield BHC.
This is also called as gammaxane or Lindane

(iii) BHC is a powerful insecticide

Benzene reacts with fuming sulphuric acid and give benzene sulphonic acid. Although S03 molecule it does not have positive charge, yet it is a strong electrophile. This is because the octet of electrons around the sulphur atom is not reacted. This reached is reversible and desulphonation occus readily in aqueous medium.

Step 1 : Formation of electrophile: In HBr, Br is more electronegative than H. When bonded electron move towards Br, polarity is developed and it creates electrophile H+ which attacks to the double bond to form a carbocation.

Step 2 : Secondary carbocation is more stable than primary carbocation and it predominates over the primary carbocation. 
Step 3 : The Bra ion attack the 2°- carbocation to form 2-Bromo propane as the major product.

(i) The compounds in which two halogen atoms are attached to adjacent carbon-atoms are called as vicinal dihalides.
(ii) When vicinal dihalides are warmed with granulated zinc in-methanol they lose a molecule of ZrtX, to form alkene
\(\underset { (1,2-dibromo\quad etane) }{ \underset { \overset { | }{ Br } }{ C } H_{ 2 }-\underset { \overset { | }{ Br } }{ C } { H }_{ 2 } } \overset { Zn|{ CH }_{ 3 }OH }{ \longrightarrow } \underset { \overset { | }{ Br } }{ C } { H }_{ 2 }-C{ H }_{ 2 }-ZnBr\longrightarrow \underset { (Ethylene) }{ { CH }_{ 2 }-{ CH }_{ 2 }+{ ZnBr }_{ 3 } } \) 

Among anthracene and cyclopentadiene - anthracene is aromatic in nature.

Anthracene		Cyclopentadiene
1.	Planar structure	Planar structure
2.	Contains 14 delocalised \(\pi\) electrons (4n + 2 = 14\(\pi\)e-)	Contains 4 non-delocalised \(\pi\) electrons
3.	Hence aromatic	Hence non-aromatic

Huckel proposed that aromaticity is a function of electronic structure. A compound may be aromatic, if it obeys the following rules
(i) The molecule must be co-planar
(ii) Complete delocalization of \(\pi\) electron in the ring
(iii) Presence of (4n+2) \(\pi\) electrons in the ring where n is an integer (n=0,1,2 .... ) is known as Huckle's rule.

1.	Cyclo penta diene	(i) It has a planar Structure (ii) It has four \(\pi\) electron but the elecron are not delocalised and hence it is not an aromatic compound.
2.	Cyclooctatetraene	Molecule is non-planar and hence it is not an aromatic compound.
3.	Cyclopropenylcation	(i) Cyclopropenyl cation has planar structure. (ii) It has 2 delocalised \(\pi\) electron. (iii) 4n + 2 = 2 4n = 0 n = 0 (an interger) and hence it is aromatic compount.

Alkyne undergoes two types of polymerisation reaction
(i) Linear Polymerisation :
Ethyne forms linear polymer, when passed into a solution of cuprous chloride and ammonium chloride.
\(2CH\equiv CH\overset { { CI }_{ 2 }/{ NE }_{ 4 }CI }{ \longrightarrow } { CH }_{ 2 }=\underset { \overset { | }{ C\equiv CH } }{ CH } \)
                                                   Vinyl ethylene
(ii) Cyclic polymerisation:
Ethyne undergoes cyclic polymerization on passing through red hot iron tube. Three molecules of ethyne polymerises to benzene.

(i) Alkenes are more reactive than alkanes due to the presence of a double bond.
(ii) The o-bond is strong but the n-bond is weak. The typical reactions of alkenes involve the addition of an electrophile across the double bond proceeding through ionic mechanism. However addition reactions proceed through free-radical mechanism also. Ozonolysis and polymerisation are some of the characteristic reaction of alkenes.