Board Paper of Class 12 2021 Chemistry Theory Term 1 Set4 code-56/1/4 - Solutions

SECTION A

(This section consists of 25 multiple choice questions with over all choice to attempt any 20 questions. In case more than desirable number of questions are attempted, only first 20 questions will be considered for evaluation.).

Question 1

Which one of the following pairs will not form an ideal solution ?

Benzene and Toluene
n-Hexane and n-Heptane
Ethanol and Acetone
Bromoethane and Chloroethane

Ans. (c)

Ethanol and acetone do not form ideal solution because hydrogen bonding between ethanol molecules is weakened by acetone which leads to positive deviation from Raoult’s law.

Solutions

Question 2

When NaCl is doped with ${SrCl}_{2}$ , there will be a formation of :

Anion vacancies
Cation vacancies
Both cation and anion vacancies
F-centre

Ans. (b)

When molten NaCl is doped with Sr²⁺, some of the Sr²⁺ ions occupy sites of Na⁺ ions creating vacancies of Na+ ions as each Sr²⁺ will replace two Na⁺ ions.

Solutions

Question 3

The structure of Oleum is:

Ans. (d)

Solutions

Question 4

The C – O – C bond angle in the ether molecule is :

111 $°$
90 $°$
120 $°$
180 $°$

Ans. (a)

Solutions

Question 5

Which of the following reagents will not convert ethyl alcohol into ethyl chloride ?

${PCl}_{5}$
$NaCl$
${SOCl}_{2}$
$HCl / {ZnCl}_{2}$

Ans. (b)

Hydroxyl group does not act as a good leaving group and does not displaced by a nucleophile. To facilitate the reaction, -OH group of alcohol is need to be protonated by an acid such as sulphuric acid.

Solutions

Question 6

Nucleotides are composed of a :

pentose sugar and phosphoric acid
nitrogenous base and phosphoric acid
nitrogenous base and a pentose sugar
nitrogenous base, a pentose sugar and phosphoric acid

Ans. (d)

Nucleotide forms DNA strand and each nucleotide is made by:

Nitrogenous base
Pentose sugar
Pentose sugar

Solutions

Question 7

The oxidation state of − 3 is least stable in :

Ans. (b)

Stability of -3 oxidation state decreases down the group due to increase in size and metallic character.

Solutions

Question 8

Amorphous solids may also be classified as

supercooled solids
superheated liquids
supercooled liquids
superheated solids

Ans. (c)

Solutions

Question 9

Which of the following reagents should be used to carry out the above conversion?

LiAlH₄
NaBH₄
Zn-Hg/HCl
KMnO₄

Ans. (b)

NaBH₄ is a weak reducing agent than LiAlH₄. It reduces only ketone group in the given compound.

Solutions

Question 10

An azeotropic solution of two liquids has a boiling point higher than either of the two when it :

shows a negative deviation from Raoult’s law
shows a positive deviation from Raoult’s law
is saturated
shows no deviation from Raoult’s law

Ans. (a)

In case of negative deviation from Raoult’s law, new bonds formed between molecules are stronger than the intermolecular forces between respective constituents. The tendency of molecules to escape decrease and boiling point increases.

Solutions

Question 11

Which of the following crystals will show metal deficiency defect ?

$NaCl$
$ZnO$
$FeO$
$AgCl$

Ans. (c)

In the crystal of FeO, some Fe²⁺ ions are missing and for the loss of every three Fe²⁺ ions, two Fe³⁺ ions present causing metal deficiency.

Solutions

Question 12

Phenol on being heated with concentrated $H_{2} {SO}_{4}$ and then with concentrated ${HNO}_{3}$ gives :

o-nitrophenol
2,4,6-trinitrophenol
p-nitrophenol
m-nitrophenol

Ans. (b)

Solutions

Question 13

$O_{3}$ reacts with KI solution to produce :

$O_{2} only$
$I_{2} only$
${KIO}_{3}$
$Both O_{2} and I_{2}$

Ans. (d)

Solutions

Question 14

α-D-Glucose and β-D-Glucose differ from each other with respect to the :

Number of – OH groups
Configuration at the C-1 carbon
Size of the hemiacetal ring
Configuration at the C-5 carbon

Ans. (b)

Solutions

Question 15

Lucas reagent produces cloudiness immediately with :

Ans. (a)

Tertiary alcohols give turbidity immediately with Lucas reagent as they form halides easily.

Solutions

Question 16

Which of the following is most reactive towards nucleophilic substitution reaction?

Ans. (d)

In case of haloarenes, presence of an electron withdrawing group (such as -NO₂) at ortho- and para- position increases their reactivity.

Solutions

Question 17

Pressure does not have any significant effect on solubility of solids in liquids because :

Solids are highly compressible
Liquids are highly compressible
Solubility of solid in liquid is directly proportional to partial pressure
Solids and liquids are highly incompressible

Ans. (d)

Solids and liquids are highly incompressible due to absence of intermolecular spaces.

Solutions

Question 18

Main product in the following reaction is:

Ans. (c)

Solutions

Question 19

Which of the following forms strong p $π$ − p $π$ bonding ?

$P_{4}$
$N_{2}$
${Sb}_{4}$
${As}_{4}$

Ans. (b)

Only nitrogen forms p $π$ —p $π$ multiple bonds due to small size and high electronegativity. Other elements of group-15 do not form p $π$ —p $π$ multiple bonds due to large and highly diffused atomic orbitals.

Solutions

Question 20

Which of the following halogens can replace all other halogens from their halidecompounds ?

$F_{2}$
${Cl}_{2}$
${Br}_{2}$
$I_{2}$

Ans.(a)

Fluorine (F) can replace all other halogens from their halide compound because of small size and high electronegativity.

Solutions

Question 21

The functional unit that is repeated in a protein molecule is :

An ester linkage
A glycosidic linkage
A peptide linkage
An ether linkage

Ans. (c)

Solutions

Question 22

The lowest boiling point of ‘He’ is due to :

Its inertness
Its high polarizability
Its small size
Weak dispersion forces between its atoms

Ans. (d)

In case of helium, only weak dispersion forces are present leading to low boiling point.

Solutions

Question 23

Major products formed by heating (CH₃)₃C – O – CH₂ – CH₃ with HI are :

Ans. (a)

Solutions

Question 24

The osmotic pressure of a solution increases if :

The volume of the solution is increased
The number of solute molecules is increased
Temperature is decreased
Solution constant (R) is increased

Ans. (b)

Solutions

Question 25

Chlorine reacts with hot and concentrated NaOH to give:

Ans. (d)

$6 NaOH + 3 {Cl}_{2} \to 5 NaCl + {NaClO}_{3} + 3 H_{2} O$

Solutions

SECTION B

(This section consists of 24 multiple choice questions with overall choice to attempt any 20 questions. In case more than desirable number of questions are attempted, only first20 questions will be considered for evaluation).

Question 26

Vapour pressure of dilute aqueous solution of glucose is 750 mm Hg at 373 K. The mole fraction of solute is :

Ans. (c)

Solutions

Question 27

The bases that are common in both DNA and RNA are :

Adenine, Guanine and Cytosine
Adenine, Guanine and Thymine
Adenine, Uracil and Cytosine
Guanine, Uracil and Thymine

Ans. (a)

Solutions

Question 28

A compound (X) with the molecular formula C₃H₈O can be oxidised to another compound (Y) whose molecular formula is C₃H₆O₂. The compound (X) may be:

Ans. (c)

Solutions

Question 29

Which reagent is required for one step conversion of benzene diazonium chloride to bromobenzene ?

${PBr}_{3}$
$HBr$
${Cu}_{2} {Br}_{2}$
${Br}_{2}$

Ans. (c)

Solutions

Question 30

The number of lone pair of electrons on $Xe$ in ${XeF}_{2}$ , ${XeF}_{4}$ and ${XeF}_{6}$ compounds are respectively :

4, 3 and 2
2, 3 and 1
3, 2 and 0
3, 2 and 1

Ans. (d)

Solutions

Question 31

Which form of sulphur shows paramagnetic behaviour ?

$S_{8}$
$S_{4}$
$S_{2}$
$S_{6}$

Ans.(c)

In vapour state of sulphur partly exists as S₂ molecule and S₂ molecule has two unpaired electrons in the anti-bonding $π^{*}$ orbitals.

Solutions

Question 32

An element with density 3 g cm^-3 forms a bcc lattice with edge length of 3 × 10^-8 cm. The molar mass of the element is: (N_A= 6 × 10²³ mol^-1)

Ans. (b)

Solutions

Question 33

In the following reaction:

Ans. (a)

Solutions

Question 34

Which of the following has the greatest reducing power ?

Ans. (a)

HI is the strongest reducing agent among halogen acids because of lowest bond dissociation energy.

Solutions

Question 35

The freezing point of a 0.2 molal solution of a non-electrolyte in water is: (K_f for water = 1.86 K kg mol^-1)

Ans. (a)

Solutions

Question 36

In a bcc structure, the packing efficiency is approximately :

Ans. (b)

Solutions

Question 37

${NO}_{2}$ gas dimerises because :

It is acidic in nature
It contains even number of valence electrons
It contains odd number of valence electrons
It is inert at room temperature

Ans. (c)

NO₂ contains odd number of valance electrons. On dimerisation, it gives N₂O₄ molecule having even number of electrons.

Solutions

Question 38

A compound forms hcp structure. The number of tetrahedral voids in 0.5 mol of it is:

Ans. (a)

Solutions

Question 39

XeF₂ on reaction with PF₅ forms:

Ans. (c)

$[X e F_{2}] + [P F_{5}] \to {[X e F]}^{+} {[P F_{6}]}^{-}$

PF₅ act as a fluoride ion acceptor.

Solutions

Question 40

Arrange the following compounds in decreasing order of their acidic character :

Ans. (b)

-NO₂ is an electron withdrawing group and stabilises the phenoxide ion while -CH₃ is an electron donating group and do not favours the phenoxide ion formation.

Solutions

Question 41

Which of the following compounds undergoes racemisation on hydrolysis with aqueous KOH?

Ans. (d)

Solutions

Question 42

Which of the following is not true ?

Fluorine exhibits only – 1 oxidation state.
Among halide ions, $I_{2}$ is the strongest oxidising agent.
F − F bond has lower bond dissociation enthalpy than Cl − Cl bond.
Fluorine forms only one oxoacid

Ans. (b)

Among halide ions, iodine is the weakest oxidising agent due to its large size.

Solutions

Question 43

The IUPAC name of isobutyl bromide is :

1-bromo-3-methylbutane
3-bromo-2-methylpropane
2-bromo-2-methylpropane
1-bromo-2-methylpropane

Ans. (d)

Solutions

Question 44

Chlorobenzene when treated with sodium in dry ether gives Diphenyl. It is called :

Wurtz reaction
Fittig reaction
Wurtz-Fittig reaction
Friedel-Crafts reaction

Ans. (b)

Solutions

Question Nos. 45 to 49 are Assertion (A) and Reason (R) type questions. Given below are two statements labelled as Assertion (A) and Reason (R). Select the most appropriate answer from the options given below

Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
Assertion (A) is true, but Reason (R) is false.
Assertion (A) is false, but Reason (R) is true.

Question 45

Assertion (A) : ${NH}_{3}$ is less basic than ${PH}_{3}$
Reason (R) : Nitrogen is more electronegative than phosphorus.

Ans. (d)

Ammonia (NH₃) is more basic than PH₃ as the size of nitrogen is smaller and electron density is more than phosphorous.

Solutions

Question 46

Assertion (A) : Osmotic pressure is a colligative property.
Reason (R) : Osmotic pressure of a solution depends on the molar concentration of solute at any temperature T

Ans. (a)

Solutions

Question 47

Assertion (A) : Aryl halides are extremely less reactive towards nucleophilic substitution reaction.
Reason (R) : Halogen atom shows +I effect in Aryl halides.

Ans. (c)

Aryl halides are extremely less reactive towards nucleophilic substitution reaction due to resonance effect.

Solutions

Question 48

Assertion (A) : Due to Frenkel defect there is no effect on density of solid.
Reason (R) : Ions shift from its normal site to an interstitial site in Frenkel defect.

Ans. (a)

Frenkel defect is also called as dislocation effect. The smaller ion (cation) is dislocated to an interstitial site and no change in density observed.

Solutions

Question 49

Assertion (A) : Ozone is a powerful oxidising agent in comparison to O₂.
Reason (R) : Ozone is thermodynamically stable with respect to oxygen.

Ans. (c)

Ozone is a powerful oxidising agent as it liberates nascent oxygen easily. Ozone is thermodynamically unstable with respect to ozone and it produces heat by decomposing to oxygen

Solutions

SECTION C

(This section consists of 6 multiple choice questions with an overall choice to attempt any 5 questions. In case more than the desirable number of questions are attempted, only the first 5 questions will be considered for evaluation).

Question 50

Match the following:

Ans. (c)

Solutions

Question 51

Which of the following analogies is correct :

Ans. (b)

Oxygen contains no d-orbital for ${dπ}^{-} pπ$ bonding.

Cl₂ is less reactive than ClF.

Xe form many compounds but He not.

Solutions

Question 52

Complete the following analogy:

Ans. (d)

ZnS - Ionic solid (contains ionic bonds as zinc is metal and sulphur is a non-metal) SiC - Covalent solid (contains covalent bonds as both elements are non-metals)

Solutions

Case – Study

Read the passage given below and answer the following question nos. 53 – 55.

Carbohydrates are polyhydroxy aldehydes or ketones and are also called saccharides. Glucose is an example of monosaccharides. Glucose (C₆H₁₂O₆) is an aldohexose and its open chain structure was assigned on the basis of many reactions as evidences like presence of carbonyl group, presence of straight chain, presence of five -OH groups, etc. Glucose is correctly named as D-(+)-Glucose. Glucose is found to exist in two different crystalline forms which are named as $α$ and $α$ . Despite having the aldehyde group, glucose does not give 2, 4-DNP test.

Question 53

Which of the following represents D-(+)-Glucose ?

Ans. (b)

Solutions

Question 54

Glucose on oxidation with ${HNO}_{3}$ gives a dicarboxylic acid called saccharic acid. This result validates the fact that Glucose possesses :

− CHO group
− OH group
Data is not made available to everybody.
both − CHO and − ${CH}_{2} OH$ groups at the terminals of the chain

Ans. (d)

Solutions

Question 55

The pentaacetate of glucose does not react with $H_{2} N$ − $OH$ indicating the absence of :

− OH group
− CHO group
− COOH group
− ${CH}_{2} OH$ group

Ans. (b)

Carbonyl group (>C=O) reacts with hydroxylamine (NH₂OH) to form an oxime. No reaction with hydroxylamine confirms absence of carbonyl group in pentacetate of glucose.

Solutions

Board Paper of Class 12 2021 Chemistry Theory Term 1 Set4 code-56/1/4 - Solutions

SECTION A

Question 1

Which one of the following pairs will not form an ideal solution ?

Question 2

When NaCl is doped with SrCl2, there will be a formation of :

Question 3

The structure of Oleum is:

Question 4

The C – O – C bond angle in the ether molecule is :

Question 5

Which of the following reagents will not convert ethyl alcohol into ethyl chloride ?

Question 6

Nucleotides are composed of a :

Question 7

The oxidation state of − 3 is least stable in :

Question 8

Amorphous solids may also be classified as

Question 9

Which of the following reagents should be used to carry out the above conversion?

Question 10

An azeotropic solution of two liquids has a boiling point higher than either of the two when it :

Question 11

Which of the following crystals will show metal deficiency defect ?

Question 12

Phenol on being heated with concentrated H2SO4 and then with concentrated HNO3 gives :

Question 13

O3 reacts with KI solution to produce :

Question 14

α-D-Glucose and β-D-Glucose differ from each other with respect to the :

Question 15

Lucas reagent produces cloudiness immediately with :

Question 16

Which of the following is most reactive towards nucleophilic substitution reaction?

Question 17

Pressure does not have any significant effect on solubility of solids in liquids because :

Question 18

Main product in the following reaction is:

Question 19

Which of the following forms strong pπ − pπ bonding ?

Question 20

Which of the following halogens can replace all other halogens from their halidecompounds ?

Question 21

The functional unit that is repeated in a protein molecule is :

Question 22

The lowest boiling point of ‘He’ is due to :

Question 23

Major products formed by heating (CH3)3C – O – CH2 – CH3 with HI are :

Question 24

The osmotic pressure of a solution increases if :

Question 25

Chlorine reacts with hot and concentrated NaOH to give:

SECTION B

Question 26

Vapour pressure of dilute aqueous solution of glucose is 750 mm Hg at 373 K. The mole fraction of solute is :

Question 27

The bases that are common in both DNA and RNA are :

Question 28

A compound (X) with the molecular formula C3H8O can be oxidised to another compound (Y) whose molecular formula is C3H6O2. The compound (X) may be:

Question 29

Which reagent is required for one step conversion of benzene diazonium chloride to bromobenzene ?

Question 30

The number of lone pair of electrons on Xe in XeF2 , XeF4 and XeF6 compounds are respectively :

Question 31

Which form of sulphur shows paramagnetic behaviour ?

Question 32

An element with density 3 g cm-3 forms a bcc lattice with edge length of 3 × 10-8 cm. The molar mass of the element is: (NA= 6 × 1023 mol-1)

Question 33

In the following reaction:

Question 34

Which of the following has the greatest reducing power ?

Question 35

The freezing point of a 0.2 molal solution of a non-electrolyte in water is: (Kf for water = 1.86 K kg mol-1)

Question 36

In a bcc structure, the packing efficiency is approximately :

Question 37

NO2 gas dimerises because :

Question 38

A compound forms hcp structure. The number of tetrahedral voids in 0.5 mol of it is:

Question 39

When NaCl is doped with ${SrCl}_{2}$ , there will be a formation of :

Phenol on being heated with concentrated $H_{2} {SO}_{4}$ and then with concentrated ${HNO}_{3}$ gives :

$O_{3}$ reacts with KI solution to produce :

Which of the following forms strong p $π$ − p $π$ bonding ?

Major products formed by heating (CH₃)₃C – O – CH₂ – CH₃ with HI are :

A compound (X) with the molecular formula C₃H₈O can be oxidised to another compound (Y) whose molecular formula is C₃H₆O₂. The compound (X) may be:

The number of lone pair of electrons on $Xe$ in ${XeF}_{2}$ , ${XeF}_{4}$ and ${XeF}_{6}$ compounds are respectively :

An element with density 3 g cm^-3 forms a bcc lattice with edge length of 3 × 10^-8 cm. The molar mass of the element is: (N_A= 6 × 10²³ mol^-1)

The freezing point of a 0.2 molal solution of a non-electrolyte in water is: (K_f for water = 1.86 K kg mol^-1)

${NO}_{2}$ gas dimerises because :

XeF₂ on reaction with PF₅ forms:

Assertion (A) : ${NH}_{3}$ is less basic than ${PH}_{3}$
Reason (R) : Nitrogen is more electronegative than phosphorus.

Assertion (A) : Osmotic pressure is a colligative property.
Reason (R) : Osmotic pressure of a solution depends on the molar concentration of solute at any temperature T

Assertion (A) : Aryl halides are extremely less reactive towards nucleophilic substitution reaction.
Reason (R) : Halogen atom shows +I effect in Aryl halides.

Assertion (A) : Due to Frenkel defect there is no effect on density of solid.
Reason (R) : Ions shift from its normal site to an interstitial site in Frenkel defect.

Assertion (A) : Ozone is a powerful oxidising agent in comparison to O₂.
Reason (R) : Ozone is thermodynamically stable with respect to oxygen.

Glucose on oxidation with ${HNO}_{3}$ gives a dicarboxylic acid called saccharic acid. This result validates the fact that Glucose possesses :

The pentaacetate of glucose does not react with $H_{2} N$ − $OH$ indicating the absence of :