(i) Recycled waste can be used as fuel. It has high octane rating and can be used as green fuel.
(ii) Clothes can be made from recycled plastic waste.
(iii) It can be used to produce electricity.

A process which can take place of its own or initiate under some condition.
For example: Common salt dissolves in water of its own.

Since the bond dissociation energy of C - C bonds (348 KJ mol^-1) is lower than bond dissociation energy of C -H bonds (414 KJ mol^-1), therefore during cracking of alkanes, C - C bonds break more easily than C - H bonds.

Rotation around C-C single bond is not completely free and it is restricted due to repulsions between the electron clouds of C-H bonds in the adjacent carbon atoms. Therefore, ethane exixts in infinate number of conformations. Out of these, two extreme conformations are staggered and eclipsed.

Total mass of organic compound = 0.468 g [Given]
Mass of barium sulphate formed = 0.668 g [Given]
1 mol of BaSO₄ = 233 g of BaSO₄=32 g of sulphur
Thus, 0.668 g of BaSO4 contains \(= \frac{32×0.668}{233}\)g of sulphur = 0.0917 g of sulphur
Therefore, percentage of sulphur \(=\frac{0.0197}{0.468}\)×100=19.59%
Hence, the percentage of sulphur in the given compound is 19.59 %.

As we move from carbon to silicon atomic size increases, i.e. the distance between the outermost electron and nucleus increases. Thus, this electron experience very small attraction from the nucleus and hence, easy to remove. Since, the size of Si-atom is larger, the outer electron experience lesser attraction and hence, its ionisation enthalpy (energy required to remove ab electron) is smaller.

\(\overset { +3-1 }{ 4BCl_{ 3 } } (g)+\overset { +1+3-1 }{ 3LiAl{ H }_{ 4 } } (s)\longrightarrow \overset { -3+1 }{ 2{ B }_{ 2 }{ H }_{ 6 } } (g)+\overset { +1-1 }{ 3LiCl } (s)+3\overset { +3-1 }{ AlC{ l }_{ 3 } } (s)\) 
Oxidation number of B decreases from +3(in BCl₃) to -3(in B₂H₆) and oxidation number of H increases from -1(in LiAlH₄) to +1 (in B₂H₆ ). This shows that BCl₃ is reduced to B₂H₄ and LiAlH₄ is oxidised. Hence, it is redox reaction.

The number designation of a group that has 2 electrons beyond a noble gas configuration will be 2 which means it will belong to group 2 of the periodic table.

|ψ|² shows the probability of finding the electron at a point with coordinates (x, y, z).

On heating red oxide of copper in the presence of hydrogen, its mass decreases and it forms shining metallic copper which is chemically different from the original compound.
Cu₂O + H₂ ⟶ 2Cu + H₂O

0.33 mol

Wurtz synthesis: Higher alkanes are prepared by heating an alkyl halide (RX) with sodium metal in dry ether solution.
R - X + 2Na + XR \(\overset { ether }{ \longrightarrow } \) R - R + 2NaX
CH₃Br + 2Na + BrCH_{3\(\longrightarrow \)} CH₃-CH₃ + 2NaBr
Limitations: Use of two different alkyl halides in Wurtz reaction always leads to a mixture of alkanes. The separation of these alkanes is difficult because there is only a little difference in their boiling points. Thus only symmetrical alkanes can be prepared by this method.

Electronic configuration of carbon atom: C: σ1s² 2s² 2p².
In the excited state, the orbital picture of carbon can be represented as:

Hence, carbon atom undergoes sp³ hybridization in CH₄ molecule and takes a tetrahedral shape.

For a square planar shape, the hybridization of the central atom has to be dsp³. However, an atom of carbon does not have d-orbitals to undergo dsp3 hybridization. Hence, the structure of CH₄ is tetrahedral.

Calculation of mass of nickel (Ni) in the alloy.
Volume of the alloy = (10.0 cm) x (20.0 cm) x (15.0 cm) = 3000cm³
Mass of the alloy = Density x Volume
Mass of Ni in the alloy = (24510 g) x\(\frac { 45.8}{ 100 } \) = 11225.6 g
Calculation of number of nickel (Ni) atoms in the alloy
Gram atomic mas of Ni = 59 g
59 g of Ni have atoms = 6.022 x 10²³
11225.6 g of Ni have atoms = 6.022 x 10²³ x\(\frac { (11.225.6 g)}{ (59.0 g) } \)= 1.15 x10²⁶atoms

Presence of electron releasing group(or activating group) increases the electron density in benzene nucleus. Therefore, electrophile will attack
benzene nucleus easily. But, the presence of electron withdrawing group like -NO₂ decrease the electron density in benzene ring. Therefore, electrophile will attack
benzene nucleus with difficulty. The order of reactivity towards electrophile, E+ in order of their decreasing relative reactivity is
(i) Chlorobenzene > p-nitrochlorobenzene > 2, 4- dinitrochlorobenzene
(ii) Toluene > \(p-{ CH }_{ 3 }-{ C }_{ 6 }{ H }_{ 4 }-{ NO }_{ 2 }>p-{ O }_{ 2 }N-{ C }_{ 6 }{ H }_{ 4 }-{ NO }_{ 2 }\)

\(PbS(s)+{ 4 }H_{ 2 }{ O }_{ 2 }(aq)\rightarrow PbSO_{ 4 }(s)+{ 4H }_{ 2 }O(l)\) (redox reaction)

According to VSEPR theory, the shape of a molecule depends upon the number shell electron pairs (bonded or non-bonded) around the central atom. Pairs of electrons in the valence shell repel each other. The order of their repulsion is as follows
 Cl, The central atom Be has only 2 valence electron which are bonded to Cl, so there are only 2 bond pairs and no lone pairs. It is of the type AB₂ and hence, the shape linear

The central atom B has only 3 valence electron which are bonded with three CI atoms, so it contains only 3 bond pairs and no longer pair. It is of the type AB₃ and hence, the shape is trigonal plannar

Similarly, the central atom Si has only 4 bond pairs and no longer pair. It is of the type AB₄ and hence, the shape is tetrahedral

The central atom As has only 5 bond pairs and no lone pair. It is of the type AB₅ and hence, the shape is trigonal bipyramidal

The central atom S has 6 valence electrons. Out of these only two are used in bond formation with two H-atoms while four(two pairs) remains as non-bonding electrons(i.e lone pairs)
So, it contains 2 bond pairs and 2 lone pairs. It is of the type AB₂E₂ and hence, the shape is bent V-shaped

The central atom P has 5 valence electrons. Out of which three are utilised in bonding with H atoms and one pair remains as lone pair
So, it contains 3 bond pairs and one lone pair. It is of the type AB₃ E and hence the shape is pyramidal.

There are numerous physical properties of elements such as melting points, boiling points, heats of fusion and vaporisation, energy of atomisation, etc., which show periodic variations. The cause of periodicity in properties is the repetition of similar outer electronic configuration after certain regular intervals. e.g. all the elements of 1s group (alkali metals) have similar outer electronic configuration, i.e. ns¹.
₃Li = 1s², 2s¹
₁₁Na = 1s², 2s², 2p⁶ , 3s¹
₁₉K = 1s², 2s², 2p⁶ , 3s², 3p⁶, 4s¹
Therefore, due to similar outermost shell electronic configuration all alkali metals have similar properties. e.g., sodium and potassium both are soft and reactive metals. They all form basic oxides and their basic character increases down the group. They all form unipositive ion by the loss of one electron. Similarly, all the elements of 17th group (halogens) have similar outermost shell electronic configuration, i.e. ns²  np⁵ and thus possess similar properties.
₉F = 1s², 2s¹ , 2p⁵
₁₇Cl = 1s², 2s², 2p⁶ , 3s² , 3p⁵
₃₅Br = 1s², 2s², 2p⁶ , 3s², 3p⁶, 3d¹⁰, 4s² , 4p⁵

Calculation of molecular formula
Empirical formula mass =
 \(2\times 56+3\times 16=160\)
\(n=\frac { molecular \ formula }{ empirical \ formula \ mass } =\frac { 160 }{ 160 } =1\)
\(\therefore Molecular\ formula={ A }_{ 2 }{ B }_{ 3 }\)

Photochemical smog consists of O₃ , NO, acrolein, formaldehyde and PAN. O₃ and NO irritate the nose and throat and their high concentration causes a headache, chest pain, dryness of throat, cough, difficulty in breathing. Aldehydes and PAN cause irritation in eyes. PAN is highly toxic substance to plants and causes bronzing of tender leaves. Ozone also affects the rubber articles and causes cracking and ageing.
Control of Photochemical smog if primary precursors of photochemical smog such as hydrocarbons and NO₂ are controlled, the secondary precursors such as O₃ and PAN will automatically be reduced.
Certain Plants such as Pinus, Junioparus etc., can metabolise nitrogen oxide and can help in reducing photochemical smog.

Pesticides These substance are used to kill or block the reproductive processes of pests. These are basically synthetic toxic chemicals with ecological repercussions. Their accumulation in higher animals causes serious metabolic and physiological disorders. DDt, aldrin, dieldrin, organophosphates and carbonates are some examples of pesticides.
Herbicides These are weed killers i.e. they kill unwanted herbs growing along with crops e.g. sodium chlorate (NaCIO₃) and sodium arsenite (Na₃AsO₃). These are toxic to mammals. Some herbicides cause birth defects. Now a days triazines, better herbicides are used for the corn fields.

The general formula of alkanes is C_nH_2n+2=12xn+1x(2n+2)=72 or 12n+2n+2=72 or n=5
Thus, the molecular formula of the alkane is C₅H₁₂. For structural isomers and their IUPAC names.

I and III, I and IV, II and III and II and IV represent chain isomerism.
a) \({ CH }_{ 3 }CO{ CH }_{ 3 }\) 
b) \(H-CH={ CH }_{ 2 }\).

The electrode potential, i.e. reduction potential of Na (-2.71 V) or K (-2.92) is much lower than that of H₂ O
(-0.83 V), therefore, upon electrolysis, water gets reduced in preference to Na⁺ or K⁺ ions. In other words, sodium and potassium cannot be obtained by electrolytic reduction of Na⁺ and K⁺ ions in aqueous solution.