ISC Class 12 Sample Paper 2025 Chemistry

isc
specimen paper
2025
ISC Study Material

CHEMISTRY
PAPER 1
(THEORY)
Maximum Marks: 70
Time Allotted: Three Hours
Reading Time: Additional Fifteen minutes

Instructions to Candidates
➢ You are allowed additional 15 minutes for only reading the question
paper.
➢ You must NOT start writing during the reading time.
➢ This question paper has 11 printed pages.
➢ It is divided into four sections and has 21 questions in all.
➢ All questions are compulsory. Answer all questions.
➢ Section A has fourteen subparts. Each question carries 1 mark.
➢ While attempting Multiple Choice Questions in Section A, you are
required to write only ONE option as the answer.
➢ Section B has ten questions. Each question carries 2 marks.
➢ Section C has seven questions. Each question carries 3 marks.
➢ Section D has three questions. Each question carries 5 marks.
➢ Internal choices have been provided in one question each in Sections B,
C and D.
➢ The intended marks for questions are given in brackets [ ].
➢ All working, including rough work, should be done on the same sheet as,
and adjacent to the rest of the answer.
➢ Balanced equations must be given wherever possible and diagrams where
they are helpful.
➢ When solving numerical problems, all essential workings must be shown.
➢ In working out problems, use the following data:
Gas constant R=1·987cal deg-1mol-1=8·314JK-1mol-1
=0·0821dm3atmK-1mol-1, 1 l atm =1dm3atm=101·3 J.
1 Faraday=96500 coulombs. Avogadro’s number= 6·023×1023.

Instruction to Supervising Examiner
➢ Kindly read aloud the Instructions given above to all the candidates present
in the examination hall.
1

SECTION A - 14 MARKS

Question 1
(A) Fill in the blanks by choosing the appropriate word(s) from those given in the [4×1]
brackets:
[four, three, remains same, propane, ns1-2, increases, six, propan-2-ol,
(n-1)d1-10, two, decreases, Clemmensen’s, Wolff-Kishner]
(i) The molar conductance of a solution _________ on dilution but the
specific conductance of a solution _________ on dilution.
(Understanding)
(ii) In the complex ion [CoCl(en)2ONO]+, the coordination number and
the oxidation number of the central metal ion are ______ and
________. (Understanding)
(iii) Propanone on reaction with zinc amalgam in the presence of
concentrated HCl gives ______ and the reaction is called _______
reduction. (Recall)
(iv) The variation and magnitude of oxidation state in coordination
complexes is due to the participation of inner ________ electrons in
addition to outer __________ electrons. (Understanding)
(B) Select and write the correct alternative from the choices given below. [7×1]
(i) The correct order of the increasing basic nature of Ammonia,
Methylamine and Aniline is: (Analysis)
(a) Methylamine < Aniline < Ammonia
(b) Aniline < Methylamine < Ammonia
(c) Ammonia < Aniline < Methylamine
(d) Aniline < Ammonia < Methylamine
(ii) Colligative properties of a solution are: (Understanding)
(P) Independent of the nature of solute
(Q) Proportional to molecular mass of solute
(R) Proportional to concentration of solute
(S) Independent of the amount of solvent
(a) Only P and Q are correct
(b) Only P and R are correct
(c) Only P and S are correct
(d) Only Q and S are correct

2

(iii) According to Markownikoff’s rule, “The negative part of the halogen acid
attaches itself with that C atom of an unsymmetrical alkene which has least
number of H-atom.”
Anti-Markownikoff’s addition of HBr is NOT observed in: (Analysis)
(a) Propene
(b) But-2-ene
(c) But-1-ene
(d) Pent-2-ene
(iv) Most of the naturally occurring α-amino acids are optically active and have
L-configuration. Which of the following amino acids is NOT asymmetric?
(Recall)
(a) Valine
(b) Alanine
(c) Glycine
(d) Leucine
(v) Which one of the following complex ions has geometrical isomers?
(Understanding)
(a) [Ni(NH3)5Br]+
(b) [Cr(NH3)4en]3+
(c) [Co(NH3)2(en)2]3+
(d) [Co(NH3)6]3+
(vi) Given below are two statements marked Assertion and Reason. Read the two
statements carefully and select the correct option.
Assertion: Tertiary butyl bromide undergoes Wurtz reaction to give 2,2,3,3
tetramethyl butane.
Reason: In Wurtz reaction, when same alkyl halides react with sodium in dry
ether to give hydrocarbon; the hydrocarbon formed contains double
the number of carbon atoms present in the alkyl halide.
(Analysis)
(a) Both Assertion and Reason are true and Reason is the correct
explanation of assertion.
(b) Both Assertion and Reason are true but Reason is not the correct
explanation for Assertion.
(c) Assertion is true but Reason is false.
(d) Both Assertion and Reason are false.

3

(vii) Given below are two statements marked Assertion and Reason. Read the two
statements carefully and select the correct option.
Assertion: There is a continuous increase in size among Lanthanoids with an
increase in atomic number.
Reason: Lanthanoids do not show Lanthanoid contraction. (Analysis)
(a) Both Assertion and Reason are true and Reason is the correct
explanation of Assertion.
(b) Both Assertion and Reason are true but Reason is not the correct
explanation for assertion.
(c) Assertion is true but Reason is false.
(d) Both Assertion and Reason are false.
(C) Read the passage carefully and answer the questions that follow. [3×1]
A plant or any other living being maintains a reasonable balance of C-14
(radioactive carbon) in its tissue during its lifetime. C-14 is used to determine
the age of fossils. In the upper atmosphere, neutrons present in the cosmic
rays are captured to produce the following nuclear reaction.
14
7N + 0n1 6C
14
+ 1H1
C-14 isotope is circulated in the atmosphere and gets absorbed by living
organism during photosynthesis. The ratio of C-14 to C-12 in living being is
1:1012. Once the living being dies, the level of C-14 in the dead being
decreases due to the following reaction.
6C
14
7N
14
+ -1e0 + γ rays
The death of the plant brings an end to its tendency to take up C-14. The half-
life period of C-14 is 5770 years. By knowing the concentration of C-14 in
the living plant and the piece of dead material at a particular time, the age of
the material (fossil) can be determined.
(i) Write the relation between the decay constant and half-life period.
(Recall)
(ii) In a piece of dead wood, the activity or concentration of C-14 is found
to be one third of its initial activity. Calculate the age of the old wood.
(Application)
(iii) The half-life period (t1/2) for a first order reaction is 30 minutes.
Calculate the time taken to complete 87·5% of the reaction.
(Application)

4

SECTION B – 20 MARKS

Question 2 [2]

The solution of two electrolytes A and B are diluted. ˄𝑚 of B increases 1·5 times while
that of A increases 25 times. Which of the two is a strong electrolyte? Give a reason.
(Understanding)

Question 3 [2]

An organic compound [A] which has characteristic odour, reacts with conc. NaOH to
give two compounds [B] and [C]. Compound [B] has molecular formula C7H8O which
upon oxidation gives back compound [A]. Compound [C] is the sodium salt of the acid
and upon treatment with sodalime yields an aromatic hydrocarbon [D]. Identify the
compounds [A], [B], [C] and [D]. (Understanding)

Question 4 [2]
Devise a scheme for the synthesis of n-butane using CH3I as the only source of carbon.
Is it possible to obtain propane in pure state by applying this scheme? Give a reason for
your answer. (Evaluate)

Question 5 [2]
It is generally observed that the rate of a chemical reaction becomes double with every
10oC rise in temperature. If the generalisation holds true for a reaction in the temperature
range of 298K to 308K, what would be the value of activation energy (Ea) for the
reaction? (Application)

Question 6 [2]
An organic compound [X] of molecular formula C3H5N, in one reaction produced a
primary amine with LiAlH4. In another case, the organic compound [Y] of same
molecular formula C3H5N produced a secondary amine with LiAlH4. Identify both the
compounds [X] and [Y]. Why do these compounds form two different products?
(Understanding)

Question 7 [2]

During chemistry class, a teacher wrote [Ni(CN)4]2- as a coordination complex ion on
the board. The students were asked to find out the magnetic behaviour and shape of the
complex. Pari, a student, wrote the answer paramagnetic and tetrahedral whereas
another student Suhail wrote diamagnetic and square planer.
Evaluate Pari’s and Suhail’s responses. (Evaluate)

5

Question 8 [2]
An organic compound ‘X’ with molecular formula C4H10O is found to be soluble in
conc.H2SO4 and does not react with sodium metal or KMnO4. Compound ‘X’ when
heated with excess of HI gives a single alkyl halide. Deduce the structure of the
compound ‘X’. Explain all the reactions involved. (Understanding)

Question 9 [2]
(i) Identify the compounds [A] and [B ] in the following reactions.
(Understanding)
(1) K2Cr2O7/H2SO4 C6H6(anhy. AlCl3)
(a) C6H5CHO [A] [B]
(2) SOCl2
(1) H2SO4/HgSO4 C2H5OH
CH3-C≡CH [A] [B]
(b) (2) vigorous oxidation, [conc. H2SO4]
conc.HNO3
OR
(ii) Three organic compounds A, B and C are non cyclic functional isomers of
carbonyl compounds with molecular formula C4H8O. Isomers A and C give
positive Tollen’s test while compound B does not give positive Tollen’s test but
gives positive iodoform test. Compounds A and B on reduction with Zn amalgam
and conc. HCl give the same product.
(a) Write the structures of the compounds A, B and C. (Understanding)

(b) Out of the compounds A, B and C, which one will be the least reactive
towards addition of HCN. (Understanding)

Question 10 [2]
Calculate the value of E cell, E cell and ∆G that can be obtained from the following cell
o

at 298K.
Al/Al3+(0.01M) // Sn2+(0.015M)/Sn
Given EoAl3+/Al = −1·66V; EoSn2+/Sn = −0·14V (Application)

Question 11 [2]
Write the chemical test to distinguish between the following pairs of compounds.
(Understanding)
(i) Propan-1-ol and Propan-2-ol

(ii) Phenol and ethanol

6

SECTION C – 21 MARKS

Question 12 [3]
Identify the compounds [A], [B] and [C] in the following reactions.
6[H] HNO2 + HCl C6H5NH2
(i) C6H5NO2 [A] [B] [C]
Sn/HCl 273K-278K
(Understanding)
(1) HNO2 (1) KCN (1) NH3/heat
(ii) CH3CH2NH2 [A] [B] [C]
(2) P/Cl2 (2) H2O/H+ (2) Br2/KOH
(Understanding)

Question 13 [3]
The molar mass calculated through colligative properties is sometimes different from
that of experimentally determined molecular mass and is known as abnormal molecular
mass. This difference is due to the solute particles that undergo association or
dissociation.
Consider the two cases given below and answer the questions that follow.
(A) The freezing point of a solution containing 5·85g of NaCl in 100g of water is
− 3·348oC. (Kfof water = 1·86 K kg mol-1, molecular mass of NaCl = 58·5)
o
(B) The freezing point of benzene solution decreases by 0·45 C when 0·2g of acetic
acid is added to 20g of benzene.
(Kfof benzene = 5·12 K kg mol-1, molecular mass of acetic acid = 60)
Answer the following questions.
(i) Calculate the abnormal molecular mass of solute in both the cases.
(Application)
(ii) Inferring the value of van’t Hoff factor in both the cases, find out which
solution undergoes association and which solution undergoes
dissociation. (Analysis)
(iii) Given below is the increasing order of depression in freezing point of
water observed for equimolar concentrations of the compounds,
acetic acid < trichloro acetic acid < trifluoro acetic acid
Provide a reason to explain if the above ordered arrangement is correct or
not. (Understanding)

Question 14 [3]
Write chemical equations to illustrate the following name reactions. (Recall)
(i) Rosenmund’s reaction
(ii) Benzoin condensation
(iii) Perkin’s reaction

7

Question 15 [3]
(i) Assuming that cyanide is a strong ligand, write the formula of two coordination
complex ions with cyanide and iron having coordination number six. Name the
complex ions. (Application)
(ii) On the basis of Crystal Field Theory, write the electronic configuration of d4 ion
if: (Application)
(a) ∆o > P
(b) ∆o< P

Question 16 [3]
(i) Dry cells are commonly used in clocks, torches, calculators etc. They are the
most familiar type of commercial cells.
(a) What acts as anode and cathode in dry cell? (Understanding)
(b) Which chemical compounds are filled between anode and cathode of this
cell? (Understanding)
(c) Why do dry cells not have a long life? (Understanding)
OR
(ii) Answer the following:
(a) What happens to the voltage when the salt bridge is removed from the two
half cells and why? (Understanding)
(b) Copper sulphate solution cannot be stored in a zinc pot. Why?
(Understanding)
(c) Why does the density of H2SO4 in a lead storage battery decrease as it is
discharged? (Understanding)

Question 17 [3]
(i) The structures of glycine and alanine are given below. Show the peptide bond
linkage in glycylalanine. (Understanding)
CH3
H2N-CH2-COOH H2N-CH-COOH
Glycine Alanine
(ii) What products would be formed when a nucleotide from DNA containing
thymine is hydrolysed? (Understanding)
(iii) What are reducing sugars? Give an example. (Recall)

8

Question 18 [3]
Consider the data given below for the reaction A + B Product
S.No. conc. of [A] mol L-1 conc. of [B] mol L-1 Rate; mol L-1sec-1
1. 0·1 0·1 4·0 × 10- 4
2. 0·2 0·2 1·6 × 10- 3
3. 0·5 0·1 1·0 × 10- 2
4. 0·5 0·5 1·0 × 10- 2
Answer the following questions.
(i) What is the order of reaction with respect to A and B? (Application)
(ii) Calculate the rate constant. (Application)
(iii) Determine the reaction rate when the concentration of A and B are
0·2 mol L-1sec-1 and 0·35 mol L-1sec-1 respectively. (Evaluate)

SECTION D – 15 MARKS

Question 19 [5]
Phenol, one of the deadliest acids, contains a hydroxy group directly attached to the
aromatic ring. A hydroxy group attached to an aromatic ring is also referred to as a
phenolic group. Due to the presence of -OH group, phenols show many reactions similar
to those of alcohols. The direct attachment of -OH group to the aromatic ring makes its
behaviour very different from that of alcohols. That is why phenol behaves differently
from alcohols in many reactions. The chemical reactions of phenol can be categorised
as follows:
• Reactions involving -OH group
• Reactions involving benzene ring
(i) Write the chemical equation for the preparation of phenol from benzene using
H2SO4 and NaOH. (Understanding)
(ii) What happens when phenol reacts with Br2/CS2 at low temperature? (Recall)

(iii) What is observed when phenol is treated with neutral ferric chloride solution?
(Recall)
(iv) Write the reaction when phenol is treated with conc. HNO3 in the presence of
conc. H2SO4. (Understanding)
(v) Write the reaction when phenol is treated with chloroform in the presence of
aqueous NaOH at 340K. (Understanding)

9

Question 20 [5]
(i) Give a reason for each of the following.

(a) The purple colour of KMnO4 disappears in the presence of acidified
solution of oxalic acid. (Understanding)
(b) Some transition metals and their compounds get attracted towards the
magnetic field. (Understanding)
(c) 2+ 2+
Why are Mn compounds more stable than Fe towards oxidation to the
+3 state? (atomic no. of Mn = 25 and Fe = 26) (Understanding)
(ii) Complete and balance the following reactions. (Recall)
(a) KMnO4 + H2SO4 + FeSO4 → ______+ ______+_____+______
(b) K2Cr2O7 + H2SO4 + KI → ______+ ______+_____+______

Question 21 [5]
(i) Osmosis and osmotic pressure play a very significant role in biological processes.
The osmotic pressure of human blood is 8·21 atm at 27oC. It is interesting to know
that a 0·91% (mass/volume) solution of NaCl, known as saline water is isotonic
with fluids inside the human red blood cells. In this solution, the blood corpuscles
neither swell nor shrink. Therefore, medicines are mixed with saline water before
being injected into the veins.
Answer the following questions.
(a) What is an isotonic solution? (Recall)
(b) How much glucose should be used per 100ml (aqueous solution) for
intravenous injection that is isotonic with blood at 27oC? (Application)
(c) What would be the osmotic pressure of blood if the temperature is 37oC?
(Application)
(d) A pure NaCl solution with salt concentration less than 0·91%
(mass/volume) is hypertonic solution to human blood. Is this statement true
or false? Give a reason. (Understanding)
(e) Name the disease caused by taking a lot of salt or salty food, which results
in water retention in tissue cells causing puffiness or swelling.
(Recall)
OR
(ii) (a) Calculate the boiling point of urea solution when 8·0g of urea is dissolved
in 250g of water. Boiling point of pure water is 373K.
(kb of water = 0·52 K kg mol-1, molecular mass of urea = 60 g mol-1)
(Application)

10

(b) Ethylene glycol is used as an antifreeze agent. Calculate the amount of
ethylene glycol to be added to four kilogram of water to prevent it from
freezing at -6oC.
(Kf of water = 1·86 K kg mol-1) Assume that ethylene glycol
(CH2OH.CH2OH) does not dissociate or associate in aqueous solution.
(Application)
(c) What will be the effect on the value of molality and molarity of a solution
with change in temperature? (Understanding)

11

CHEMISTRY
ANSWER KEY
SECTION A - 14 MARKS

Question 1
(A) (i) increases, decreases [4×1]
(ii) six, three
(iii) propane, Clemmensen’s
(iv) (n-1)d 1-10,ns 1-2
(B) (i) (d) or Aniline < Ammonia < Methylamine [7×1]
(ii) (b) or Only P and R are correct
(iii) (b) or But-2-ene
(iv) (c) or Glycine
(v) (c) or [Co(NH3)2(en)2]3+
(vi) (a) or Both Assertion and Reason are true and Reason is the correct
explanation of assertion.
(vii) (d) or Both Assertion and Reason are false.
(C) (i) 0.693 [3×1]
k = t½

(ii) 9146·5 years
(iii) 90·03 minutes

SECTION B – 20 MARKS

Question 2 [2]
B is strong because on dilution ˄𝑚 increases to a little extent.

Question 3 [2]
[A] =C6H5CHO [B] = C6H5CH2OH [C] = C6H5COONa [D] = C6H6

Question 4 [2]
Carry out Wurtz reaction twice
No, propane cannot be prepared in fairly pure state.

ISC SPECIMEN ANSWER KEY 2025
1

Question 5 [2]
Ea = 52897.78 J

Question 6 [2]
[A] = C2H5CN , on reduction gives primary amines.
[B] = C2H5NC , on reduction gives secondary amines.

Question 7 [2]
According to Valence Bond Theory (VBT) [Ni(CN)4]2- is diamagnetic and square planar.
Suhail’s response was correct.

Question 8 [2]
[X] = C2H5OC2H5
C2H5OC2H5 +2HI ------→ 2 C2H5I + H2O

Question 9 [2]
(i) (a) [A] = C6H5COCl [B] = C6H5COC6H5
(b) [A] = CH3COOH [B] = CH3COOC2H5
OR
(ii) (a) [A] = CH3CH2CH2CHO [B] = CH3COCH2CH3
[C] = CH3CH(CH3)CHO
(b) [B] will be least reactive towards addition of HCN

Question 10 [2]
E0cell = 1.52 V, Ecell = 1.5056 V, ΔG = -871742 Joules

Question 11 [2]
(i) Luca’s reagent test
(ii) Bromine water test / Ferric Chloride test / Esterification test

SECTION C – 21 MARKS

Question 12 [3]
(i) [A] = C6H5NH2 [B] = C6H5N2Cl [C] = C6H5N =NC6H4NH2
(ii) [A] = CH3CH2Cl [B] = CH3CH2COOH [C] = CH3CH2NH2

ISC SPECIMEN ANSWER KEY 2025
2

Question 13 [3]
(i) molecular mass [A] =32.5 [B] =113.79
(ii) [A] undergoes Dissociation while [B] undergoes Association
(iii) The given order of depression in freezing point is correct, as ΔTf depends on the
number of moles of solute.

Question 14 [3]
(i) RCOCl +H2 Pd/BaSO4, heat RCHO + HCl
(ii) C6H5CHO + C6H5CHO KCN(alc) C6H5CH(OH)COC6H5
(iii) C6H5CHO +(CH3CO)2O CH3COONa C6H5CH =CHCOOH + CH3COOH
Heat

Question 15 [3]
(i) [Fe(CN)6]4- , hexacyanidoferrate(II)ion
[Fe(CN)6]3- , hexacyanidoferrate(III)ion
(ii) (a) Δ0> P, low spin, strong field, t2g4eg0
(b) Δ0<P, high spin, weak field, t2g3eg1

Question 16 [3]
(i) (a) Anode is Zn and graphite rod is cathode.
(b) Moist paste of ZnCl2 and NH4Cl.
(c) NH4Cl paste in dry cell is acidic in nature and corrodes the Zn container.
OR
(ii) (a) The voltage drops to zero, as current will stop flowing in the circuit of the
cell.
(b) No, zinc is placed above copper in electrochemical series.
(c) During discharge(use) of the battery H2SO4 is used up, as a result density
decreases.

Question 17 [3]
(i) NH2CH2COOH + NH2CH(CH3)COOH NH2CH2[CONH ]CH(CH3)COOH
+H2O
Glycine alanine glycylalanine
(ii) β-D-2 deoxyribose sugar, the base residue A,G,C and T + phosphate.
(iii) Carbohydrates which are capable of reducing Tollen’s reagent and Fehling’s
solution. For example, glucose and fructose.

ISC SPECIMEN ANSWER KEY 2025
3

Question 18 [3]
(i) Order with respect to [A] is 2 and with respect to [B] is 0.
(ii) Rate constant (k) = 4 X 10-2 mol-1 L sec-1
(iii) Rate =1·6 × 10-3 mol L-1 sec-1

SECTION D – 15 MARKS

Question 19 [5]
(i) (a) Equation required with proper catalyst and by product
Benzene Benzene sulphonic acid sodium benzene sulphonate
sodium phenoxide phenol
(b) o-bromophenol and p- bromophenol is formed
(c) Violet/ purple colour solution is obtained
(d) 2,4,6 tri nitro phenol is formed
(e) Salicylaldehyde is formed

Question 20 [5]
+7 +2
(i) (a) Oxidation state of Mn changes from Mn (purple) to Mn (colourless).
(b) Due to the presence of unpaired electrons in d-orbital.
(c) Mn2+ has half filled d-orbitals (d5)while Fe2+ had (d6) configuration
(ii) (a) 2KMnO4 + 8H2SO4 +10FeSO4→ K2SO4+2MnSO4 +5Fe2(SO4)3 +8 H2O
(b) K2Cr2O7 + 7H2SO4 + 6KI → 4K2SO4 +Cr2(SO4)3 +3I2 +7H2O

Question 21 [5]
(i) (a) Definition of Isotonic solution.
(b) w = 6 gram of glucose
(c) π = 8.48 atm.
(d) False,it is hypotonic.
(e) Edema
OR
(ii) (a) Boiling point of Urea solution = 373.277 K
(b) Amount of Ethylene glycol = 800g
(c) Molality is not affected by change in temperature. Molarity of a solution
decreases on increasing the temperature due to increase in volume.

ISC SPECIMEN ANSWER KEY 2025
4

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