(i) Ⓐ of molecular formula CH₂O is identified as HCHO, formaldehyde.
(ii) Formaldehyde reacts with CH₃MgI followed by hydrolysis to give ethanol, CH₃- CH₂OH B as the product.

(iii) Ethanol Ⓑ, reacts with PCl₅ to give C₂H₅CI, Ethyl chloride © as the product.

(iv) CH₃-CH₂CI © on reaction with alcoholic KOH undergoes dehydrohalogenation to give ethylene CH₂ = CH₂ © as the product.
\(CH_{ 3 }-{ CH }_{ 2 }Cl\overset { alcoholic }{ \underset { KOH }{ \longrightarrow } } \underset { Ethlene }{ { CH }_{ 2 }={ CH }_{ 2 }+HCl } \)

(i) When half filled orbitals of two atoms overlap, a covalent bond will be formed between them.
(ii) The resultant overlapping orbital is occupied by the two electrons with opposite spins. For example, when H₂ is formed, the two Is electrons of two hydrogen atoms get paired up and occupy the overlapped orbital.
(iii) The strength of a covalent bond depends upon the extent of overlap of atomic orbitals. Greater the overlap, larger is the energy released and stronger will be the bond formed.
(iv) Each atomic orbital has a specfic direction (except s-orbital which is spherical) and hence orbital overlap takes place in the direction that maximizes overlap.

Rain water normally has a pH of 5.6 due to dissolution of atmospheric CO₂ into it. Oxides of sulphur and nitrogen in the atmosphere may be absorbed by droplets of frater that make up clouds and get chemically converted into sulphuric acid and nitric acid respectively as a results of pH of rain water drops below the level 5.6, hence it is called acid rain. Acid rain is a by-product of a variety of sulphur and nitrogen oxides in the atmosphere. Burning of fossil fuels (coal and oil) in power stations, furnaces and petrol, diesel in motor engines produce sulphur dioxide and nitrogen oxides The main contributors of acid rain are SO₂ and NO₂.They are converted into sulphuric acid and nitric acid respectively by the reaction with oxygen and water.
2SO₂ + O₂ + 2H₂O ⟶ 2H₂SO₄
4NO₂ + O₂ + 2H₂O ⟶ 4HNO₃
Harmful effects of acid rain
Some harmful effects are discussed below :
(i) Acid rain causes extensive damage to buildings and structural materials of marbles. This attack on marble is termed as Stone leprosy.
CaCO₃ + H₂SO₄ ⟶ CaSO₄ + H₂O +CO₂ ↑
(ii) Acid rain affects plants and animal life in aquatic ecosystem.
(iii) It is harmful for agriculture, trees and plants as it dissolves and removes the nutrients needed for their growth.
(iv) It corrodes water pipes resulting in the leaching of heavy metals such as iron, lead and copper into the drinking water which have toxic effects.
(v) It causes respiratory ailment in humans and animals.

w = 0.2 g ,N = 1/20 N, v = 15 ml
\(\mathrm{V}=15 \mathrm{ml} \% \mathrm{~N}=\frac{1.4 \mathrm{NV}}{\mathrm{W}}=\frac{1.4 \times 1 / 20^{\times 15}}{0.2}=5.25 \%\)

\(\Delta T_f=0.093^oC=0.093K\)
m = ?
K_f = 1.86K Kg mol^-1
\(\Delta T_f=K_f.m\)
\(\therefore m={\Delta T_f\over K_f}\)
\(={0.093K\over 1.86\ K\ Kg\ mol^{-1}}\)
= 0.05 mol Kg^-1
= 0.05 m.

Characteristics of entropy:
(i) Entropy is a thermodynamic state function that is a measure of the randomness or disorderliness of the system.
(ii) In general, the entropy of gaseous system is greater than liquids and greater than solids. The symbol of entropy is S.
(iii) Entropy is defined as for a reversible change taking place at a constant temperature (T), the change in entropy (\(\Delta\)S) of the system is equal to heat energy absorbed or evolved (q) by the system divided by the constant temperature (T).
 \(\Delta S_{sys}=\frac{q_{rev}}{T}\)
(iv) If heat is absorbed, then \(\Delta\)S is positive and there will be increase in entropy. If heat is evolved, \(\Delta\)S is negative and there is a decrease in entropy.
(v)The change in entropy of a process represented by \(\Delta\) S and is given by the equation.
 \(\Delta S_{sys}=S_f-S_i\)
(vi) If S_f > S_i, \(\Delta\)S is positive, the reaction is spontaneous and reversible.
If S_f < S_i, \(\Delta\)S is negative, the reaction is non-spontaneous and irreversible.
(vii) Unit of entropy: SI unit of entropy is J K^-1.

Empirical formula = C₂H₅NO
Molecular mass = 2 x vapour density
= 2 x 29.5 = 59.0
Empirical formula mass of C₂H₅NO = 24 + 5 + 14 +16
= 59
n = \({Molecular \ mass \over Empirical \ formula \ mass }={59\over 59}=1\)
\(\therefore\) Molecular formula = (Empirical formula)_n
= (C₂H₅NO)₁
Molecular formula = C₂H₅NO

(i) An element A belonging to II group and II period is beryllium (A)
(ii)  Beryllium reacts with chlorine to form beryllium chloride (B)
Be +Cl₂ \(\longrightarrow \) BeCl₂
                         (B)
(iii) Beryllium chloride on treatment with LialH Forms beryllium hydride (c)
2BeCl₂ + LiA1H₄ \(\longrightarrow \) 2BeH₂ + LiCl + AlCl₃ 
                                                             (C)

The electronic configuration of K atom is
K₁₉ = (1s²)(2s²p⁶)(3s²3p⁶)4s¹
Effective nuclear charge (Z*) = Z - S
Z* = 19 - [(0.85 \(\times\) No. of electrons in (n -1)t^h shell) + (1.00 total number of electrons in the inner shells)]
= 19-[0.85 \(\times\) (8) + (1.00 \(\times\) 10)]
Z* =  2.20

The element which occupies group number (16) and period number (2) is oxygen. (B) is D₂O which is used as a moderator in nuclear reactions.
So (A) must be deuterium, which is an isotope of hydrogen
    \(2\underset { (A) }{ { D }_{ 2 } } +{ O }_{ 2 }\rightarrow 2\underset { (B) }{ { D }_{ 2 }O } \)
So (B) is D₂O
(A) adds to (C) as follows :
\(3 \mathrm{D}_{2}+\mathrm{C}_{3} \mathrm{H}_{6} \rightarrow \mathrm{CH}_{3}-\mathrm{CH}-\mathrm{CH}_{2}\)
So (D) is 1,2 - dideutero propane. 

The word Aufbau in German means 'building up'. In the ground state of the atoms, the orbitals are filled in the order of their increasing energies. That is the electrons first occupy the lowest energy orbital available to them.
Once the lower energy orbitals are completely filled, then the electrons enter the next higher energy orbitals. The order of filling of various orbitals as per the Aufbau principle which is in accordance with (n + l) rule.

(i) The energy of electrons in atoms is quantised
(ii) The existence of quantized electronic energy levels is a direct result of the wave like properties of electrons. The solutions of Schrodinger wave equation gives the allowed energy levels (orbits).
(iii) According to Heisenberg uncertainty principle, the exact position and momentum of an electron can not be determined with absolute accuracy. As a consequence, quantum mechanics introduced the concept of orbital. Orbital is a three dimensional space in which the probability of finding the electron is maximum.
(iv) The solution of  Schrodinger wave equation for the allowed energies of an atom gives the wave function ψ,which represents an atomic orbital. The wave nature of electron present in an orbital can be well defined by the wave function ψ.
(v) The wave function ψ itself has no physical meaning.However, the probability of finding the electron in a small volume dxdydz around a point (x,y,z) is proportional to |ψ(x,y,x)|² dxdydz |ψ(x,y,x)|² is known as probability density and is always positive.

(i) The arrangement of atoms must be identical or almost same in every resonance structure.
(ii) The energy content of all the canomical forms must be almost same.
(iii) Each canocial form must have the same number of unpaired electrons.

Al₄C₃ + 12D₂O ➝ 4AI(OD)₃ + 3CD₄
Aluminium Heavy  Aluminium   Deutero
carbide      water   deuteroxide  Methane
CaC₂ + D₂O ➝ Ca(OD)₂ + C₂D₂
Calcium            Calcium       Deutero
Carbide           deuteroxide  acetylene
Mg₃N₂ + 6D₂O ➝ 3Mg(OD)₂ + 2ND₃
Magnesium          Magnesium  Deutero
Nitride                  deuteroxide​​​​​​​  ammonia​​​​​​​
Ca₃P₂ + 6D₂O ➝ 3Ca(OD)₂ + 2PD₃
Calcium              Calcium        Deutero
Phosphide         deuteroxide   Phosphine

P_Ne = X_Ne P_Total
\(X_{Ne}=\frac{n_{Ne}}{n_{Ne}+n_{Ar}+n_{Xe}}\)
\(=\frac{4.76}{4.76+0.74+2.5}=0.595\)
\(X_{Ar}=\frac{n_{Ar}}{n_{Ne}+n_{Ar}+n_{Xe}}\)
 \(=\frac{0.74}{4.76+0.74+2.5}=0.0093\)
\(X_{Xe}=\frac{n_{Xe}}{n_{Ne}+n_{Ar}+n_{Xe}}\)
\(=\frac{2.5}{4.76+0.74+2.5}=0.312\)
P_Ne = X_Ne P_Total = 0.595 x 2
= 1.19 atm.
P_Ar = X_Ar P_Total = 0.093 x 2
= 0.186 atm.
P_Xe = X_Xe P_Total = 0.312 x 2
= 0.624 atm.

Apple turns brown when cut since the surface is exposed to air and undergoes oxidation. It can be prevented by dipping sliced apples in lemon juice. Lemon juice is an antioxidant which takes in all the available oxygen and prevents it from reaching the apple's tissues

T_i = 298 K
T_f = 298.45 K
k = 2.5 kJK^-1
m =3.5g
M_m = 28
heat evolved= kΔT
=k (T_f - T_i)
=2.5 KJ K^-1 (298.45 - 298)K
=1.125kJ
ΔH_c=\(\frac{1.125}{3.5}\times\)28KJmol^-1
ΔH_c = 9 kJ mol^-1

(i) Lithium and beryllium form more covalent compounds, unlike the alkali and alkali earth metals which predominantly form ionic compounds.
(ii) The elements of the second period have only four orbitals (2s & 2p) in the valence shell and have a maximum co-valence of 4, whereas the other members of the subsequent periods have more orbitals in their valence shell and shows higher valences. For example, boron forms BF₄^- and aluminium forms AIF₆^3-.

In ferrocynide ion [Fe(CN)₆]^4-, each cyanide ion (CN-) donates a pair of electrons to form a co-ordinate bond with iron (Fe²⁺) and these electrons are shared by Fe²⁺ and CN^-.

In certain cases, molecules having a lone pair of electrons such as ammonia donates its pair to an electron deficient molecules such as B₃ to form a co-ordinate bond.

This condition is not static and is dynamic, because both the forward and reverse reactions are still occurring with the same rate. No macroscopic change is observed.

(i) Heat (q) is regarded as energy in transit across the boundary separating a system from its surroundings.
(ii) Heat changes result in temperature differences between system and surroundings.
(iii) Heat is a path function.
(iv) Units of heat: SI unit of heat is the joule (J).

Molar Mass of Al(OH)₃ = \(\begin{cases} atomic\ \ mass\ 'al'+3x\ atomic\ \ mass\ \ of \ 'O' \\ +3x\ atomic\ \ mass\ \ of\ \ 'h' \end{cases}\)
= 27 + 3\(\times\)16 + 3\(\times\)1 = 78
Acidity = 3
Equivalent mass of AL(OH)₃ = \(\frac { Molar\quad mass }{ acidity } =\frac { 78 }{ 3 } =26geq^{ -1 }\)

The real gases behave ideally at low pressure and at high temperature.

The solubility product of NaCl is lower than that of NaOH. The more soluble a substance is, the higher the K_sp value it has In aqueous solution NaOH gives OH^- ions. It can be solvated by establishing H-bonds with water molecules. So it is more water soluble.

(i) ground state :

This type of electronic configuration have ten possible arrangement (i.e. Half filled configuration is More).

2Ca + O₂ ⟶ 2CaO