(i) HOCI in presence of an acid generates the reactive electrophile, chloronium ion «r, which attacks benzene to give chlorobenzene (A).
(ii) Chlorobenzene (A) on treatment with NaNH2/liq. NH₃ undergaes-dehydrohalogenation via benzyne to afford aniline (B).
(iii) Aniline (B) on treatment with HBF4 forms the corresponding salt anilinium tetrafluoroborate (C) which on heating with NaNO₂ undergoes Balz-Schiemann reaction through the intermedium formation of benzenediazonium tetrafluoroborate to afford fluorobenzene (D).

We know that S_N2 reactions proceed with inversion of configuration at the stereocentre. If, however, two S_N2 reactions are carried out at the same stereocentre of a compound, retention of configuration will occur. Thus, (R)-2-octanethiol can be obtained from (R)-2-bromooctane by first reacting it with Nal in acetone and then with NaSH in ethanol

tert-Alkyl halides prefer to undergo dehydrohalogenation in presence of a strong base such as Na metal instead of undergoing Wurtz reaction as explained below:
\(\underset{tert-Butyl\ bromide}{(CH_3)_3C-Br}+2Na\longrightarrow\underset{tert-Butylsodium}{(CH_3)_3Na^+}+Na^+Br^-\)
Thus, only rand 2° alkyl halides undergo Wurtz reaction while 3° alkyl halides prefer to undergo dehydrohalogenation to form alkenes.

According to the question,
The relative ratios of these two isomeric chlorobutanes can be easily calculated by knowing: (i) the number and type of hydrogens (i.e. 1°, 2° or 3°) to be substituted and (ii) their relative rates of substitution (i.e. I : 3·8 : 5·0 for CI₂ at 298 K). Thus
\({1-Chlorobutane\over 2-Chlorobutane}={No.\ of\ 1^0H\over No.\ of\ 2^0H}\times{Reactivity\ o\ 1^0H\over Reaativity\ of\ 2^0H}={6\over 4}\times{1\over 3.8}={6\over 15.2}={28./.\over 72./.}\)

Free radical halogenation is not a suitable method for laboratory synthesis of alkyl halides because of the following two reasons :
(i) It gives a mixture of isomeric monohalogenated products whose boiling points are so close that they cannot be easily separated in the laboratory.
(ii) Polyhalogenation may also occur to some extent thereby making the mixture more complex and hence more difficult to separate.