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Chemistry (Class XII)
(I) Read the passage given below and answer the following questions:
In spite of the predictions of stable noble gas compounds since at least 1902, unsuccessful
attempts at their synthesis gave rise to the widely held opinion that noble gases are not only
noble but also inert
...
This discovery triggered a
worldwide frenzy in this area, and within a short time span many new xenon, radon, and
krypton compounds were prepared and characterized
...
The discovery by Seppelt’s group that more than one xenon atom
can attach itself to a metal center which in the case of gold leads to surprisingly stable Au- Xe
bonds
...

(Source: Christe, K
...
(2001)
...
Angewandte Chemie
International Edition, 40(8), 1419-1421
...
In the complex ion [AuXe4]2+ , Xe acts as :
a
...
ligand
c
...
electrophile
2
...
sp3
b
...
sp3d2
d
...
Compounds of noble gases except _______ are known
...
Krypton
b
...
Helium
d
...
Xe is a ___________ ligand
a
...
bidantate
c
...
hexadentate
ANSWERS : 1a, 2 b 3 c 4 c

(II) Read the passage given below and answer the following questions:
Boiling point or freezing point of liquid solution would be affected by the dissolved solids in
the liquid phase
...
The addition of non-volatile substances to a solvent decreases
the vapor pressure and the added solute particles affect the formation of pure solvent crystals
...
This phenomenon is expressed as freezing
point depression and it is useful for several applications such as freeze concentration of liquid
food and to find the molar mass of an unknown solute in the solution
...
This is done by cooling the liquid food below the freezing point of the solution
...
These are physical characteristics of solutions that depend
only on the identity of the solvent and the concentration of the solute
...
(Jayawardena, J
...
E
...
, Vanniarachchi, M
...
G
...
A
...
(2017)
...
)
1
...
boil above 100oC and freeze above 0oC
b
...
boil above 100oC and freeze below 0oC
d
...
Colligative properties are:
a
...

b
...

c
...

d
...

3
...

The concentration of sample A, B and C are 0
...
5M and 0
...
Freezing
point will be highest for the fruit juice:
a
...
B
c
...
All have same freezing point
4
...
freezing point
b
...
osmotic pressure
d
...
If the species chosen is a reactant which has a concentration c at time t the rate is dc/dt, while the rate with reference to a product having a concentration x at time t is dx/dt
...
For gas reactions pressure units are sometimes used in place of concentrations, so that
legitimate units for the rate would be (mm
...
sec-1
The order of a reaction concerns the dependence of the rate upon the concentrations of
reacting substances; thus, if the rate is found experimentally to be proportional to the α th
power of the concentration of one of the reactants A, to the β th power of the concentration of
a second reactant B, and so forth, via
...

(Laidler, K
...
, & Glasstone, S
...
Rate, order and molecularity in chemical
kinetics
...
)
In the following questions, a statement of assertion followed by a statement of reason is
given
...

A
...

B
...

C
...

D
...

1
...

Reason: Rate of reaction is a measure of change in concentration of product with
respect to time
...
Assertion: For a reaction: P +2Q  Products, Rate = k [P]1/2[Q]1 so the order of
reaction is 1
...

3
...

Reason: The unit of k is moles L-1s-1
...
Assertion: Reactions can occur at different speeds
...

Ans: 1B 2C 3D 4B

(IV) Read the passage given below and answer the following questions:
Reduction of carboxylic acids and their derivatives plays an important role in organic
synthesis, in both laboratory and industrial processes
...
A much more attractive, atom-economical approach is a catalytic reaction
using H2; however, hydrogenation of carboxylic acid derivatives under mild conditions is a
very challenging task, with amides presenting the highest challenge among all classes of
carbonyl compounds
...
C-O cleavage of amides can also be affected with silanes as reducing agents
...
3)
...
The reaction proceeds under mild pressure and
neutral conditions, with no additives being required
...


(Balaraman, E
...
, Shimon, L
...
, & Milstein, D
...
Direct
hydrogenation of amides to alcohols and amines under mild conditions
...
)
In the following questions, a statement of assertion followed by a statement of reason is
given
...

A
...

B
...

C
...

D
...


1
...

2
...

Reason: Hydride catalyst or hydrogen cause to reduction of amides
...
Assertion: N-methyl ethanamide on reaction with catalyst 3 will yield ethanol and
methanamine
...
Assertion: Aniline can be prepared from suitable amide using catalyst 3
Reason: The use of catalyst 3 is limited to aliphatic amides only
...
However, which mechanism it is based on is related to such factors as the
structure of haloalkane, and properties of leaving group, nucleophilic reagent and solvent
...
This is
just the opposite of the situation that nucleophilic reagent attacks the central carbon atom
with electron pair
...
The alkalinity order of
halogen ion is I− < Br− < Cl− < F− and the order of their leaving tendency should be I− > Br−
> Cl− > F−
...
In addition, if the leaving group is very
easy to leave, many carbocation intermediates are generated in the reaction and the reaction is
based on SN1 mechanism
...

Influences of solvent polarity: In SN1 reaction, the polarity of the system increases from the
reactant to the transition state, because polar solvent has a greater stabilizing effect on the
transition state than the reactant, thereby reduce activation energy and accelerate the reaction
...
At this time, polar solvent has a great
stabilizing effect on Nu than the transition state, thereby increasing activation energy and
slow down the reaction rate
...
The reaction rate (SN2) of 2-bromopropane and NaOH in ethanol
containing 40% water is twice slower than in absolute ethanol
...
Generally
speaking, weak polar solvent is favorable for SN2 reaction, while strong polar solvent is
favorable for SN1 reaction, because only under the action of polar solvent can halogenated
hydrocarbon dissociate into carbocation and halogen ion and solvents with a strong polarity is
favorable for solvation of carbocation, increasing its stability
...

(Ding, Y
...
A Brief Discussion on Nucleophilic Substitution Reaction on Saturated
Carbon Atom
...
312, pp
...
Trans Tech
Publications Ltd
...
SN1 mechanism is favoured in which of the following solvents:
a
...
carbon tetrachloride
c
...
carbon disulphide
2
...
1-Chloro-2,2-dimethyl propane

b
...
1-Bromo-2,2-dimethyl propane
d
...
SN1 reaction will be fastest in which of the following solvents?
a
...
Ethanol (dielectric constant 24)
c
...
Chloroform (dielectric constant 5)
4
...
destabilize transition state and decrease the activation energy
b
...
stabilize transition state and increase the activation energy
d
...
SN1 reaction will be fastest in case of:
a
...
1-Iodo-2-methyl propane
c
...
1-Iodobutane
Ans: 1 c, 2b, 3 c, 4c, 5 b

(VI) Read the passage given below and answer the following questions:
Within the 3d series, manganese exhibits oxidation states in aqueous solution from +2 to +7,
ranging from Mn2+(aq) to MnO− 4 (aq)
...
Cr and Mn form oxyions CrO2− 4 , MnO− 4 , owing to their
willingness to form multiple bonds
...
The highest oxidation states of
the 3d metals may depend upon complex formation (e
...
, the stabilization of Co3+ by
ammonia) or upon the pH (thus MnO42− (aq) is prone to disproportionation in acidic
solution)
...
The ability of
transition metals to exhibit a wide range of oxidation states is marked with metals such as
vanadium, where the standard potentials can be rather small, making a switch between states
relatively easy
...
A
...
Lanthanides: Comparison to 3d metals
...
)
In the following questions, a statement of assertion followed by a statement of reason is
given
...

A
...

B
...

C
...

D
...

1
...

Reason: The highest oxidation state exhibited corresponds to number of (n-1)d electrons
...
Assertion: Fe3+ is more stable than Fe2+
Reason: Fe3+ has 3d5 configuration while Fe2+ has 3d6 configuration
...
Assertion: Vanadium had the ability to exhibit a wide range of oxidation states
...

4
...


5
...

Reason: The number of electrons in the (n-1)d and ns subshells determine the oxidation states
exhibited by the metal
...
c 2 a 3 a 4 b 5d

(VII) Read the passage given below and answer the following questions:
Reductive alkylation is the term applied to the process of introducing alkyl groups into
ammonia or a primary or secondary amine by means of an aldehyde or ketone in the presence
of a reducing agent
...
The principal variation excluded is that in which the reducing agent is formic
acid or one of its derivatives; this modification is known as the Leuckart reaction
...
The reaction
usually is carried out in ethanol solution when the reduction is to be effected catalytically

RCHO + NH3

RCHOHNH2

2[H]

RCH2NH2
2[H]

RCH= NH

Since the primary amine is formed in the presence of the aldehyde it may react in the same
way as ammonia, yielding an addition compound, a Schiff's base (RCH= NCH2R) and
finally, a secondary amine
...


RCH=NH + RCH2NH2

RCHNHCH2R

2[H]

(RCH2)2NH + NH3

NH2
(RCH2)2NH + RCHO

(RCH2)2NCHR 2[H]

(RCH2)3N + H2O

OH
(RCH2)2N + RCH=NH

(RCH2)2NCHR

2[H]

(RCH2)3N + NH3

NH2

Similar reactions may occur when the carbonyl compound employed is a ketone
...
S
...
The Preparation of Amines by Reductive Alkylation
...
doi:10
...
or004
...
Ethanal on reaction with ammonia forms an imine (X) which on reaction with nascent
hydrogen gives (Y)
...

A
...

C
...


X
X
X
X

is CH3CH=NH and Y is CH3NH2
is CH3CHOHNH2 and Y is CH3CH2NH2
is CH3CHOHNH2 and Y is CH3NH2
is CH3CH=NH and Y is CH3CH2NH2

Q2
...
The primary amine so formed further reacts with acetaldehyde
...

B
...

D
...
The reaction of ammonia and its derivatives with aldehydes is called:
A
...

C
...


Nucleophilic substitution reaction
Electrophilic substitution reaction
Nucleophilic addition reaction
Electrophilic addition reaction

Q4
...

B
...

D
...
Reductive alkylation of ammonia by means of an aldehyde in presence of hydrogen as
reducing agents results in formation of:
A
...

C
...


Primary amines
Secondary amines
Tertiary amines
Mixture of all three amines

(Ans: 1D,2B,3C,4 A,5D)

(VIII) Read the passage given below and answer the following questions:
Some colloids are stable by their nature, i
...
, gels, alloys, and solid foams
...
The solid and liquid phases in a gel are interdispersed
with both phases being continuous
...
If a particular ion is preferentially adsorbed on the
surface of the particles, the particles in suspension will repel each other, thereby preventing
the formation of aggregates that are larger than colloidal dimensions
...
e
...
Accumulation of charge on a surface is not
an unusual phenomenon-dust is attracted to furniture surfaces by electrostatic forces
...
This phenomenon is called flocculation, and
the suspension can be referred to as flocculated, or colloidally unstable
...
The original and restored colloidal systems are called
deflocculated, peptized, or stable sols
...
Van der Waals forces are responsible for the attractions,
while the repulsive forces are due to the surface charge on the particles
...
The magnitude of the
electrical repulsion is diminished by addition of ionized salt, which allows the dispersed
particles to aggregate and flocculate
...
A
delta is formed at the mouth of a river because the colloidal clay particles are flocculated
when the freshwater mixes with the salt water of the ocean
(source: Sarquis, J
...
Colloidal systems
...
doi:10
...
Gelatin is a ________________ colloidal system
...

B
...

D
...
Colloidal solutions are stable due to:
A
...

C
...


presence of charges on the colloidal particles
formation of aggregates by colloidal particles
preferential adsorption on the surface
preferential absorption on the surface

Q3
...

B
...

D
...
When Van der Waals forces are greater than forces due to the surface charge on the
particles,
A
...

C
...


flocculation occurs
...

peptization takes place
...


Q5
...
This statement explains:
A
...

C
...


formation of delta
river water is a colloidal of clay particles
effect of salt on lyphobic colloid
phenomenon of flocculation

(Ans: 1C, 2C, 3A,4A,5B)

(IX) Read the passage given below and answer the following questions:
Industrially widely applied esterification reactions are commonly catalysed using mineral
liquid acids, such as sulphuric acid and p-toluenesulphonic acid
...
They suffer, however, from several drawbacks, such as their
corrosive nature, the existence of side reactions, and the fact that the catalyst cannot be easily
separated from the reaction mixture
...
Solid acid catalysts are not corrosive and,
coated onto a support, they can be easily reused
...
Ion-exchange resins are the most common heterogeneous
catalysts used and have proven to be effective in liquid phase esterification and etherification
reactions
...

Shortcomings include insufficient thermal resistance, which limits the reaction temperature to
120 oC, preventing widespread use in industry
...
Zeolites have found wide application in oil refining, petrochemistry and in the
production of fine chemicals
...

In this study, the activity of various commercial available solid acid catalysts is assessed with
respect to the esterification of acetic acid with butanol
...
Comparative esterification
experiments have been carried out using the homogeneous catalysts sulphuric acid, ptoluenesulphuric acid and a heteropolyacid (HPA)
...

The following table gives the activity of different catalysts in the esterification reaction
between acetic acid and butanol at 750C
...
, BENES, N
...
, & KEURENTJES, J
...
Comparison
of commercial solid acid catalysts for the esterification of acetic acid with butanol
...
doi:10
...
apcata
...
09
...
Which of the following are heterogeneous catalysts for esterifctaion reaction:

A
...

C
...


sulphuric acid and p-toluenesulphonic acid
sulphuric acid and niobium acid
p-toluenesulphonic acid and niobium acid
niobium acid and sulphated zirconia

Q2
...

B
...

D
...
The catalytic activity of homogeneous catalysts is high
...
Smopex-101
B
...
sulphated ZrO2

D
...
The weight-based activity of the heterogeneous catalysts tested decreases in the
following order:
A
...
5 > HMOR-45 > Nb2O5 > H-ZSM-5-12
B
...
5 > HMOR-45 > H-ZSM-5-12> Nb2O5
C
...
5 >
Nb2O5> H-MOR-45 > H-ZSM-5-12
D
...
5 > HMOR-45 > H-ZSM-5-12> Nb2O5
Q5
...

B
...

D
...
They can be produced by biological systems (i
...

microorganisms, plants and animals), or chemically synthesized from biological materials
(e
...
, sugars, starch, natural fats or oils, etc
...

Biodegradable biopolymers (BDP) are an alternative to petroleum-based polymers
(traditional plastics)
...
In principle the properties relevant for application as well as
biodegradability are determined by the molecular structure
...

Polylactic acid (PLA) is an example of biopolymer
...
Generally,
there are two major routes to produce polylactic acid from the lactic acid (CH3CH(OH)COOH)monomer
...
This approach produces a low to intermediate molar
mass polymer
...
This intermediate is
readily purified by vacuum distillation
...
By controlling the purity of the
dimer it is possible to produce a wide range of molar masses
...

The primary biodegradability of PLA was tested using hydrolysis tests at various composting
temperatures and pH
...
The degradation rate is very slow in ambient temperatures
...
As a result, it is
poorly degraded in landfills and household composts, but is effectively digested in hotter
industrial composts
...
, Kantorová, M
...
, Řezanka, T
...

(2003)
...
Folia Microbiologica, 48(1), 27–
44
...
1007/bf02931273 )
In the following questions, a statement of assertion followed by a statement of reason is
given
...

A
...

B
...


C
...

D
...

Q1
...

Reason: Microorganisms bring about degradation of biopolymers
...
Assertion: Lactic acid on polymerisation forms

Reason: PLA is used in producing geotextiles
...
Assertion: Lactic acid undergoes condensation polymerisation
Reason: Lactic acid is a bifunctional monomeric unit
...
Assertion:
...

Reason: PLA is a thermoplastic
...
Assertion: PLA is poorly degraded in landfills
...

(ANS: 1D, 2B, 3A,4B,5A)

(XI) Read the passage given below and answer the following questions:
In the last 10 years much has been learned about the molecular structure of elemental sulfur
...
It is known that at high temperature, the equilibrium
composition allows for a variety of rings and chains to exist in comparable concentration, and
it is known that at the boiling point and above, the vapor as well as the liquid contains small
species with three, four, and five atoms
...
Thus, sulfur atoms S2
and S3 have physical and chemical properties analogous to those of oxygen and ozone
...
S3 , thiozone has a wellknown uv spectrum, and has a bent structure, analogous to its isovalent molecules 03, SO2,
and S20
...
The most frequently quoted explanation is based on the
electron structure of the atom
...

(source: Meyer, B
...
Elemental sulfur
...
doi:10
...
Choose the correct answer out of the following choices on the basis of the above
passage
...
Assertion and reason both are correct statements and reason is correct
explanation for assertion
...
Assertion and reason both are correct statements but reason is not correct
explanation for assertion
...
Assertion is correct statement but reason is wrong statement
...
Assertion is wrong statement but reason is correct statement
...

Reason: S2 has properties analogous to O2
...
Assertion: Thiozone has bent structure like ozone
...

Q3
...

Q4
...

Reason: 3d and 4s orbitals of Sulphur have same energy
...
ATP captures chemical energy obtained from the breakdown of food molecules and
releases it to fuel other cellular processes
...
The phosphate tail of ATP is the actual power source
which the cell taps
...
Usually only the outer phosphate is removed from ATP to yield
energy; when this occurs ATP is converted to adenosine diphosphate (ADP), the form of
the nucleotide having only two phosphates
...
The primary
mechanism whereby higher organisms, including humans, generate ATP is through
mitochondrial oxidative phosphorylation
...
The first produces 2 mol of ATP per mol of glucose, and the second 36 mol
of ATP per mol of glucose
...

The efficiency of glucose metabolism is the ratio of amount of energy produced when 1 mol
of glucose oxidised in cell to the enthalpy of combustion of glucose
...
This heat is responsible for keeping us warm
...
, & Silver, I
...
(1989)
...
Journal of Cerebral
Blood Flow & Metabolism, 9(1), 2–19
...
org/10
...
1989
...
britannica
...
Cellular oxidation of glucose is a:
A
...

C
...


spontaneous and endothermic process
non spontaneous and exothermic process
non spontaneous and endothermic process
spontaneous and exothermic process

Q2
...
3kcal)

A
...

C
...


100%
38%
62%
80%

Q3
...
ATP is a nucleoside made up of nitrogenous base adenine and ribose sugar
...
ATP consists the nitrogenous base, adenine and the sugar, deoxyribose
...
ATP is a nucleotide which contains a chain of three phosphate groups bound to
ribose sugar
...
The nitrogenous base of ATP is the actual power source
...
Nearly 95% of the energy released during cellular respiration is due to:
A
...

C
...


glycolysis occurring in cytosol
oxidative phosphorylation occurring in cytosol
glycolysis in occurring mitochondria
oxidative phosphorylation occurring in mitochondria

Q5
...
ATP is a nucleotide which has three phosphate groups while ADP is a nucleoside
which three phosphate groups
...
ADP contains a nitrogenous bases adenine, ribose sugar and two phosphate groups
bound to ribose
...
ADP is the main source of chemical energy in living matter
...
ATP and ADP are nucleosides which differ in number of phosphate groups
...
38 ATP x 7
...
Glucose has 686 kcal
...
) ,3C,4D,5B)

(XIII) Read the passage given below and answer the following questions:
The transition metals when exposed to oxygen at low and intermediate temperatures form
thin, protective oxide films of up to some thousands of Angstroms in thickness
...
They range from metallic to
semiconducting and deviate by both large and small degrees from stoichiometry
...
The crystal structures are often classified by
considering a cubic or hexagonal close-packed lattice of one set of ions with the other set of
ions filling the octahedral or tetrahedral interstices
...
These distortions depend not only
on the number of d-electrons but also on the valence and the position of the transition metal
in a period or group
...
W
...
J
...
Oxidation properties
of transition metals
...
)
In the following questions, a statement of assertion followed by a statement of reason is
given
...

A
...

B
...

C
...

D
...

1
...

2
...

Reason: Ligand field effect cause distortions in crystal structures
...
Assertion : Transition metals form protective oxide films
...

4
...

Reason: Transition metal oxide may be hexagonal close-packed lattice of oxide ions with
metal ions filling the octahedral voids
...
As all the d block elements are metallic, the term d-block metals is
synonymous
...
Inclusion of the elements zinc, cadmium and mercury is necessary as some
properties of the group 12 elements are appropriate logically to include with a discussion of
transition metal chemistry
...
His horizontal table of the
elements was an attempt to group the elements together so that the chemistry of elements
might be explained and predicted
...
Mendeleev recognized that certain properties of elements
in Group VIII are related to those of some of the elements in Group VII and those at the start
of the next row Group I
...
(source: Winter, M
...
(2015)
...
27)
...
)

In the following questions, a statement of assertion followed by a statement of reason is
given
...

A
...

B
...

C
...

D
...

1
...

Reason: Transition metals are those which have incompletely filled d shell in their
compounds
...
Assertion: All d block elements are metallic in nature
...

3
...

Reason: Group I –VIII in Mendleev periodic table is divided into two subgroups, A and B
...
Assertion: Nickel is a transition element that belongs to group 10 and period 4 of the
modern periodic table
...
As shown in Figure 1 it consists
of a very long chain, the backbone of which is made up of alternate sugar and phosphate
groups, joined together in regular 3' 5' phosphate di-ester linkages
...
Two of
these---adenine and guanine--- are purines, and the other two thymine and cytosine-are
pyrimidines
...
It
should be noted that the chain is unbranched, a consequence of the regular internucleotide
linkage
...
Thus, DNA has some features which are regular, and some
which are irregular
...
These techniques indicate that DNA is a very asymmetrical
structure approximately 20 A wide and many thousands of angstroms long
...
Surprisingly each of these measurements tend to suggest that the DNA is
relatively rigid, a puzzling finding in view of the large number of single bonds (5 per
nucleotide) in the phosphate-sugar back bone
...


Figure 1
( source: Watson, J
...
, & Crick, F
...
(1953, January)
...
In Cold
Spring Harbor symposia on quantitative biology (Vol
...
123-131)
...
)
1
...

B
...

D
...
DNA molecule has ___________ internucleotide linkage and __________ sequence of the
different nucleotides
A
...
regular , irregular
C
...
irregular , irregular
3
...
phosphate -purine
B
...
phosphate- sugar
D
...
Out of the four different kinds of nitrogenous bases which are commonly found in DNA,
___________ has been replaced in some organisms
...

B
...

D
...
Starch, glycogen, cellulose, and chitin are
examples of polysaccharides
...
Amylose is soluble in water and can be hydrolyzed into glucose units
breaking glycocidic bonds, by the enzymes α- amylase and β-amylase
...
Amylopectin is a branched chain polymer of several D-glucose molecules
...
Plants are able to synthesize glucose, and the excess
glucose is stored as starch in different plant parts, including roots and seeds
...
The cells can
then absorb the glucose
...
It is structurally quite similar to amylopectin
...
It is stored in liver and skeletal muscles
...
The cell walls of plants are mostly
made of cellulose, which provides structural support to the cell
...

Like amylose, cellulose is a linear polymer of glucose
...
Every other glucose monomer in cellulose is flipped over and packed tightly as
extended long chains
...
Cellulose passing through our digestive system is called dietary fiber
...
libretexts
...
In animals , Glycogen is stored in :
A
...

C
...

2
...
straight chain , water insoluble component of starch ,which constitutes 20 % of it
...
straight chain , water soluble component of starch ,which constitutes 20 % of it
...
branched chain , water insoluble component of starch ,which constitutes 80 % of
it
...
branched chain , water soluble component of starch ,which constitutes 80 % of it
...


Which biopolymer breaks down to release glucose , whenever glucose levels drop in
Our body :
A
...
cellulose
C
...


D
...
Peptide linkage
B
...
Hydrogen bonds
D
...
Cellulose on complete hydrolysis yields:
A
...
amylopectin
C
...
amylose and amylopectin
(ANS 1 A,2B,3D, 4D,5C)



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