MBOSE Class 12 Question Paper 2025 for Chemistry

Meghalaya Board of School Education

QUESTION
PAPERS

Total No. of Printed Pages—12
HS/XII/Sc/Ch/25

2025

CHEMISTRY

Full Marks : 70

Time : 3 hours

The figures in the margin indicate full marks for the questions

General Instructions :
(i) Attempt all parts of a question together in one place.
(ii) All questions are compulsory.
(iii) Section—A : Question Nos. 1 to 5 are of multiple choice
type, each carrying 1 mark.
(iv) Section—B : Question Nos. 6 to 12 are of short answer-
type questions and carry 2 marks each.
(v) Section—C : Question Nos. 13 to 24 are also short
answer-type questions and carry 3 marks each.
(vi) Section—D : Question Nos. 25 to 27 are long answer-type
questions and carry 5 marks each.
(vii) There is no overall choice. However, an internal choice
has been provided in four questions of 2 marks, four
questions of 3 marks, and all three questions of 5 marks
weightage. Students have to attempt only one of the
choices in such questions.

/230 [ P.T.O.

( 2 )

(viii) Use of non-programmable ordinary scientific calculators
and log tables are allowed.

(ix) Mobile phones and pagers are not allowed inside the
Examination Hall.

SECTION—A
( Marks : 5 )

Choose and write the correct answers for the following in
the answer script :

1. Which of the following colligative properties is used to
determine molar masses of proteins, polymers or other
macromolecules?

(a) Depression in freezing point

(b) Relative lowering of vapour pressure

(c) Osmotic pressure

(d) Elevation in boiling point 1

2. The amount of electricity required to deposit 1 mol of
aluminium from a solution of AlCl 3 will be

(a) 0·33 faraday

(b) 1 faraday

(c) 3 faraday

(d) 1 ampere 1

HS/XII/Sc/Ch/25/230 [ Contd.

( 3 )

3. How many ions are produced from the complex
[ Co(NH 3 )6 ]Cl2 in solution?
(a) 6
(b) 3
(c) 4
(d) 2 1

4. The coordination number of Fe in [ Fe(C2O4 )3 ]3- is

(a) 2
(b) 3
(c) 4
(d) 6 1

5. When phenol is treated with CHCl 3 and NaOH, the
product formed is
(a) benzaldehyde
(b) salicylaldehyde
(c) salicylic acid
(d) benzoic acid 1

SECTION—B
( Marks : 14 )

6. Either

(a) A reaction is second-order with respect to a
reactant. How is the rate of reaction affected if the
concentration of the reactant is (i) doubled and
(ii) reduced to half? 2

HS/XII/Sc/Ch/25/230 [ P.T.O.

( 4 )

Or

(b) For a first-order reaction, show that time required for
99% completion is twice the time required for the
completion of 90% of the reaction. 2

7. What is the effect of temperature on the rate constant of a
reaction? How can this effect of temperature on rate
constant be represented quantitatively? 1+1=2

8. Either

(a) What are interstitial compounds? Why are such
compounds well-known for transition metals? 1+1=2

Or

(b) Explain giving reasons : 1×2=2

(i) Ti 3+ salts are purple whereas Ti4 + salts are
colourless.

(ii) Transition metals and their many compounds
act as good catalyst.

9. Either

(a) Give evidence that [ Co(NH 3 )5 Cl ]SO4 and
[ Co(NH 3 )5 SO4 ]Cl are ionization isomers. 2

Or

(b) [ NiCl4 ]2- is paramagnetic while [ Ni(CO)4 ] is
diamagnetic though both are tetrahedral. Explain
why. 2

HS/XII/Sc/Ch/25/230 [ Contd.

( 5 )

10. Either

(a) Show how are the following alcohols prepared by the
reaction of a suitable Grignard reagent on methanal?
1×2=2
(i) CH3—CH—CH2OH
CH3

CH2OH

(ii)

Or

(b) The following is not an appropriate reaction for the
preparation of tert-butyl ethyl ether :
CH3 CH3
C2H5ONa + CH3—C—Cl CH3—C—OC2H5
CH3 CH3

(i) What would be the major product of this
reaction? 1

(ii) Write a suitable reaction for the preparation of
tert-butyl ethyl ether. 1

11. (a) Name the vitamin whose deficiency causes rickets. 1

(b) What is the basic structural difference between
starch and cellulose? 1

12. Differentiate between globular proteins and fibrous
proteins. 2

HS/XII/Sc/Ch/25/230 [ P.T.O.

( 6 )

SECTION—C
( Marks : 36 )

13. Either
(a) What do you mean by abnormal molecular mass? 1

(b) Calculate the molality of 2·5 g of ethanoic acid
(CH 3COOH) in 75 g of benzene. 2

Or

(c) Why do gases always tend to be less soluble in
liquids as the temperature is raised? 1

(d) 1·00 g of a non-electrolyte solute dissolved in 50 g of
benzene lowered the freezing point of benzene by
0·40 K. Find the molar mass of the solute. (K f of
benzene is 5·12 K kg mol -1) 2

14. (a) What are hypertonic solutions? 1

(b) Define Raoult’s law for a solution containing a non-
volatile solute. 1

(c) Under what condition do non-ideal solutions show
positive deviation from Raoult’s law? 1

15. Either

(a) Consider the following reaction :
Cr2O27- + 14H + + 6e - ® 2Cr 3 + + 7H2O
What is the quantity of electricity in coulombs
needed to reduce 1 mol of Cr2O2-
7 ? 1

HS/XII/Sc/Ch/25/230 [ Contd.

( 7 )

(b) The molar conductivity of 0 × 025 mol L-1
methanoic acid is 46 ×1 S cm2 mol -1. Calculate
its degree of dissociation and dissociation
constant. Given lº (H + ) = 349 × 6 Scm2 mol -1 and
lº (HCOO - ) = 54 × 6 S cm2 mol -1. 2

Or

(c) Calculate the equilibrium constant of the reaction
Cu (s) + 2Ag + (aq) ® Cu2 + (aq) + 2Ag (s)
º
Given, E cell = 0 × 46 V. 1

(d) A solution of Ni (NO 3 )2 is electrolyzed between
platinum electrodes using a current of 5 amperes for
20 minutes. What mass of Ni is deposited at the
cathode? (At. mass of Ni = 58 × 7) 2

16. (a) A first-order reaction is found to have a rate
constant, k = 5 × 5 ´ 10 -14 s -1. Find the half-life of the
reaction. 1

(b) Derive the integrated rate equation for first-order
reaction. 2

17. (a) Draw a figure to show the splitting of d-orbitals in an
octahedral crystal field. 1

(b) Draw structures of geometrical isomers of
[ Fe(NH 3 )2 (CN)4 ]- . 1

(c) Write the IUPAC name of the following coordination
compound : 1
[ Co(NH 3 )5 (CO 3 )]Cl

HS/XII/Sc/Ch/25/230 [ P.T.O.

( 8 )

18. Either

(a) In the following pairs of halogen compounds, which
compound undergoes faster SN1 reaction? 1
Cl Cl
and

(b) Explain why—

(i) alkyl halides, though polar, are immiscible with
water;

(ii) Grignard reagent should be prepared under
anhydrous conditions. 1+1=2

Or

(c) What is Wurtz-Fittig reaction? 1

(d) The treatment of alkyl chlorides with aqueous KOH
leads to the formation of alcohols but in the presence
of alcoholic KOH, alkenes are the major products.
Explain. 2

19. Draw the structures of major monohalo products in each
of the following reactions : 1×3=3

OH
(i) + SOCl2 ?

CH3
(ii) + HI ?
–
N+
2X
KI
(iii) ?

HS/XII/Sc/Ch/25/230 [ Contd.

( 9 )

20. Either

(a) Give the IUPAC name of the following compound : 1
CH3—CH—CH—CH—CH2OH
Cl CH3 CH3

(b) Write the equations of the following reactions : 2

(i) Nitration of anisole

(ii) Bromination of phenol in CS2 at 273 K

Or

(c) Give the equations of reactions for the preparation of
phenol from cumene. 1

(d) Write the mechanism of the following reaction : 2
H2SO4
C2H5OH CH 2=CH2
443 K

21. (a) Arrange the following compounds in increasing order
of their boiling points : 1
CH 3CHO, CH 3CH2OH, CH 3OCH 3 , CH 3CH2CH 3

(b) What is aldol condensation? Give a reaction between
two ethanals to illustrate aldol condensation. 1+1=2

22. (a) Give one chemical test to distinguish between an
aromatic primary amine from an aliphatic primary
amine. 1

(b) Write the structure and IUPAC name of the amine
produced by the Hofmann degradation of benzamide. 1

HS/XII/Sc/Ch/25/230 [ P.T.O.

( 10 )

(c) Arrange the following in decreasing order of their
basic strength : 1
C 6H 5NH2 , C2H 5NH2 , (C2H 5 )2 NH , NH 3

23. (a) Why cannot aromatic primary amines be prepared by
Gabriel phthalimide synthesis? 1

(b) Diazonium salts of aromatic amines are more stable
than those of aliphatic amines. Give reason. 1

(c) Ethylamine is soluble in water whereas aniline is not.
Explain. 1

24. (a) What is invert sugar? 1

(b) How do you explain the amphoteric behaviour of
amino acids? 2

SECTION—D
( Marks : 15 )

25. Either

(a) What is a fuel cell? 1

(b) Represent the cell in which the following reaction
takes place :
Mg (s) + 2Ag + (0 × 0001 M ) ® Mg 2 + (0 ×130 M ) + 2Ag (s)
º
Calculate its E cell if E cell = 3 ×17 V. 2

(c) Write the chemistry of recharging the lead storage
battery, highlighting all the materials that are
involved during recharging. 2

HS/XII/Sc/Ch/25/230 [ Contd.

( 11 )

Or

(d) How much electricity in terms of Faraday is required
to produce 20 × 0 g of calcium from molten CaCl2 ?
(At. mass of Ca = 40 g mol -1) 2

(e) Define conductivity and molar conductivity for the
solution of an electrolyte. 2

(f) Why does conductivity of a solution decrease with
dilution? 1

26. Either

(a) Which is a stronger reducing agent Cr 2+ or Fe 2+
and why? 1

(b) Calculate the ‘spin only’ magnetic moment of
M2+ (aq) ion. (Z = 27) 1

(c) Mention the steps involved in the preparation of
K 2Cr2O 7 from sodium chromate. What is the effect of
increasing pH on a solution of K 2Cr2O 7 ? 2+1=3

Or

(d) What is the general electronic configuration of
d-block elements? 1

(e) Draw the structure of Cr2O2-
7 ion. 1

(f) Mention any one cause of lanthanoid contraction. 1

(g) How does the acidified permanganate solution react
with (i) Fe 2+ ion and (ii) H2S ? 1+1=2

HS/XII/Sc/Ch/25/230 [ P.T.O.

( 12 )

27. Either
(a) Which of the following acids is more stronger? Why? 1

F3C— —COOH Or H3C— —COOH

(b) What is Clemmensen reaction? Give relevant
equation involved. 1

(c) Formic acid reduces Tollens’ reagent whereas acetic
acid does not. Why? 1
(d) Why are aldehydes more reactive than ketones
towards nucleophilic addition reaction? 2

Or

(e) What types of aldehyde undergo Cannizzaro
reaction? 1
(f) Carboxylic acid is a stronger acid than phenol.
Explain why. 2

(g) Identify the products A, B, C and D from the following
reactions : 1×2=2

CH3 NH2NH2 KOH/ethylene glycol
(i) C=O A B
CH3 heat

COOH
PCl5 H2/Pd/BaSO4/S
(ii) C D

HHH

HS/XII/Sc/Ch/25/230 K25—5660

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