(i) Tetrachloroethene, CI₂C = CCI₂ is suspected to be carcinogenic and also contaminates the ground water. This harmful effect will be prevented by using liquefied CO₂ along with suitable detergent
(ii) Use of liquefied CO₂ along with detergent will not be completely safe because most of the detergents are non-biodegradable and they cause water pollution. Moreover, liquefied CO₂ will ultimately enter into the atmosphere and contribute to the green house effect.

Alkenes are rich source of loosely held \(\pi \) electrons, due to which they show electrophilic addition reaction. Electrophilic addition reactions of alkenes are accompanied by large energy changes so these are energetically favourable than that of Electrophilic substitution reactions.
In special conditions alkenes also undergo free radical substitution reactions.
In arenes during electrophilic addition reactions aromatic character of benzene ring is destroyed while during electrophilic substitution reactions of areans are enegetically more favourable than that of electrophilic addition reaction.
That's why alkenes prefer to undergo electrophilic addition reaction while arenes prefer electrophilic substitution reactions.

(a) CH₃OH as it lacks \(\pi \) -electrons hence it will not exist as resonance hybrid.
(b) CH₃CH = CHCH₂NH₂ As the lone pair of electrons on the N-atom is not conjugated with the -electrons of the double bond, thus, resonance is not possible and hence no resonance hybrid will exist.

In silicon, vacant 3d orbitals are available due to which it can accomodate electrons from six fluorine atoms, there by forming   [SiF₆]^2- ion.However in case of C only 2p² filled orbitals are available thus, it cannot expand their covalency more than 4. That why.[CF₆]^2- is not known.

Peroxide ions react with water to form H₂O₂,
\({ O }_{ 2 }^{ 2- }\)  + 2 H₂ O  \(\longrightarrow \) 2OH^- + H₂O₂

Hydrogen because of the presence of only one electron in the valence shell can either lose or gain or share it to acquire noble gas, i.e. helium gas, configuration. Therefore, in principle, it can form either ionic or covalent bonds. But the ionisation enthalpy of His very high (1312 kJmol^-1) and its electron gain enthalpy is only slightly negative (-73 kJmol^-1). As a result, it does not have a high tendency to form ionic bonds but rather prefers to form only covalent bonds.

18.0 g H₂O = 1 mol H₂O
Enthalpy change for vaporising 1 mole of H₂O = 40.79 KJ
\(\therefore \) Enthalpy change for vaporising 2 moles of 
H₂O = 2 x 40.79 KJ = 81.58 KJ
Standard enthalpy of vaporisation at 100^oC and 1 bar pressure,
\({ \triangle }_{ vap }{ H }^{ \circ }=+40.79 \ KJ \ { mol }^{ -1 }\)

Frequency, \(v=\frac { c }{ \lambda } \)
\(\because \) 1 nm = 10^-9m
\(\therefore \) 580nm = 580 x 10^-9 m = 580 x 10^-7cm
\(v=\frac { 3.0\times 10^{ 8 }{ ms }^{ -1 } }{ 580\times { 10 }^{ -9 }m } =5.17\times { 10 }^{ 14 }{ s }^{ -1 }\)
\( [Velocity \ of \ light=3\times { 10 }^{ 8 }{ ms }^{ -1 }]\)
Wave number,
 \(\bar { v } =\frac { 1 }{ \lambda } =\frac { 1 }{ 580\times 10^{ -7 }cm } \)
\( =1.724\times { 10 }^{ 4 }cm^{ -1 }\)

(A) \(\lambda =300nm=300\times { 10 }^{ -9 }m\)
(B) \(\lambda =300\mu m=300\times { 10 }^{ -6 }m\)
(C) \(\lambda =3nm=3\times { 10 }^{ -9 }m\)
(D) \(\lambda =30\overset { \circ }{ A } =30\times { 10 }^{ -9 }m=3\times { 10 }^{ -9 }m\)
\(\because \) Energy, \(E=\frac { hc }{ \lambda } orE\propto \frac { 1 }{ \lambda } \) 
\(\therefore \) Increasing order of energy is B