Ambident Nucleophile- An anionic nucleophile, which has two nucleophilic centers, or two negative sites is known as an ambident nucleophile. This negative charge is delocalized due to resonance.
Example – Cyanide and Thiocyanate are examples of ambident nucleophiles. 
^-C≡N   ↔   :C=N^-
S=C=N^- ↔  ^-S - C≡ N

CH₃−CH(Cl)CH₂CH₃ will be more easily hydrolysed because it will form secondary carbocation which is more stable than primary carbocation.

(I) Unimolecular nucleophilic substitution reaction (S_N1): Those substitution reactions in which rate of reaction depends upon the concentration of only one of the reactants, i.e. alkyl halides are called S_N1 reactions, e.g. hydrolysis of tertiary butyl chloride follows S_N1 reaction. This reaction takes place in two steps. The first step involves formation of carbocation.
The slowest step is rate determining step which involves one species only. Therefore, the rate of reaction depends only on the concentration of tertiary butyl chloride. Tertiary halides follow S_N1 mechanism. Polar protic solvents like 'fater and alcohol favour SN1 because they stabilize carbocation by solvation.
(ii) Bimolecular nucleophilic substitution reaction (S_N2): The reaction whose rate depends on the concentration of two species, alkyl halide and nucleophile. They involve one step mechanism. Back side attack of nucleophile and departing of leaving group take place simultaneously.

Non-polar solvents favour S_N2 mechanism. Primary halides follow S_N2 mechanism.

Since the hydrocarbon gives a single monochloride all the I8H atoms are equivalent. This means it has six \({ CH }_{ 3 }\) groups attached to the interlinked C atoms.
Therefore, its structure is
 \({ CH }_{ 3 }-\overset { \underset { | }{ { CH }_{ 3 } } }{ \underset { \overset { | }{ { CH }_{ 3 } } }{ C } } -\overset { \underset { | }{ { CH }_{ 3 } } }{ \underset { \overset { | }{ { CH }_{ 3 } } }{ C } } -{ CH }_{ 3 }\)

A hydrocarbon with the molecular formula, C₅H₁₀ belongs to the group with a general molecular formula CnH2n. Therefore, it may either be an alkene or a cycloalkane. Since hydrocarbon does not react with chlorine in the dark, it cannot be an alkene. Thus, it should be a cycloalkane. Further, the hydrocarbon gives a single monochloro compound, C₅H₉Cl by reacting with chlorine in bright sunlight. Since a single monochloro compound is formed, the hydrocarbon must contain H−atoms that are all equivalent. Also, as all H−atoms of a cycloalkane are equivalent, the hydrocarbon must be a cycloalkane. 

(i) The polyhalogen compound for which Paul Muller was awarded the Nobel Prize is DDT. (Dichlorodiphenyltrichloroethane). The structure of DOT is given below:
(ii) The use of DOT is banned in some countries because:
(a) it is toxic to aquatic life.
(b) it is not degraded rapidly by soil microorganisms due to its complex structure.
(c) it is not metabolized rapidly by animals and deposited in the fatty tissues.
(d) Because of its stability, it accumulates in food chain leading to biomagnification. 
(iii) Environmental protection and sensitivity towards life.

The reactions are given above:
(i) 1-methylcyclohexene is the major product.
Only one alkene is formed at beta H atoms on either side of Br atoms are equivalent.

(ii) 2-methyl-2-butene is the major product.
Two different alkenes are formed. More substituted alkene is the major product as it is more stable. This is in accordance with Saytzeff's rule.

(iii) 3,4,4-Trimethylpent-2-ene is the major product.
Two different alkenes are formed. More substituted alkene is the major product as it is more stable. This is in accordance with Saytzeff's rule.