Chemistry Sample Question Paper for Class 12th | CBSE Sample Question Paper 

HALF YEARLY EXAMINATION –2021

SUBJECT – CHEMISTRY

CLASS –XII

Time: 1: 30 minutes                                                          M.M. : 35
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General instructions :

(1) There are 35 questions in this question paper .

(2) All the questions carry equal marks .

(3) The students will mark their answers on the OMR sheet only .

(4) Each question has four possible answers – A,B,C and D. The students have to choose the most appropriate answer .

(5) The answer should be filled in the OMR sheet by darkening the ovals .

(6) Only a blue or black ballpoint pen for marking the answer .

(7) There will be no negative marking .

(8) Students will have to submit the OMR sheets to the invigilator before leaving the examination hall .

(9) Any kind of rough work should be done in the B-sheets provided .

MCQ TYPE QUESTIONS

Q.1 Which of the following is true about the value of Refractive Index of glass ?

(a) Same in all directions   

(b) different in different directions

(c) cannot be measured     

(d) always zero

Q.2 The preservation of meat by salting and of fruits by adding sugar protects them from bacterial actions because :

(a) bacteria die of eating sugar or salt

(b) due to osmosis bacteria lose water and die

(c) bacteria get stuck to the salt or sugar and die

(d) due to osmosis bacteria gain water and die

Q.3 Which oxide of nitrogen is obtained by heating ammonium nitrate ?

(a) nitric oxide 

(b) nitrous oxide 

(c) nitrogen dioxide 

(d) dinitrogen tetroxide

Q.4 Bromination of methane in presence of sunlight is a –

(a) nucleophilic substitution 

(b) free radical substitution

(c) electrophilic substitution 

(d) nucleophilic addition

Q.5 Graphite cannot be classified as :

(a) conducting solid 

(b) network solid 

(c) covalent solid 

(d) molecular solid

Q. 6 Which amino acid can be synthesized in the body ?

(a) Alanine 

(b) Lysine 

(c) Valine 

(d) Histidine

Q.7 What will be the molarity of 30 ml of 0.5 M H2SO4 solution diluted to500 ml ?

(a) 0.3 M 

(B) 0.03 M 

(C) 3 M 

(d) 0.103 M

Q.8 A nucleoside on hydrolysis , gives :

(a) an aldopentose and a nitrogenous base

(b) an aldopentose and phosphoric acid

(c) an aldopentose , a nitrogenous base and phosphoric acid

(d) a nitrogenous base and phosphoric acid

Q,9. Which of the following crystals does not exhibit Frenkel defect ?

(a) AgBr 

(b) AgCl 

(c) KBr 

(d) ZnS

Q.10 The oxyacid of sulphur that contains a lone pair of electrons on sulphur , is :

(a) sulphurous acid

(b) sulphuric acid

(c) peroxodisulphuric acid

(d) pyrosulphuric acid

Q.11 Identify the products (A) and (B) in the reactions :

RX + AgCN è (A) + AgX

RX + KCN è (B) + KX

(a) (A) – RCN (B) – RCN 

(b) (A)—RCN (B) –RNC

(c) (A)—RNC (B) –RCN 

(d) (A) –RNC (B) – RNC

Q.12 ------ is identified by the use of Lukas Reagent .

(a) Nitroalkane 

(b) Alkene 

(c) Alcohol 

(d) Alkyl halide

Q.13 If 1 g of solute (molar mass = 50 gram per mole )is dissolved in 50 g of solvent and the elevation of boiling point is 1K , the Molal elevation constant of the solvent is :

(a) 2                (b) 3                (c) 2.5                (d) 5

Q.14 Identify A , B and C :

A + ( CH3MgBr) à B + ( H3O+) à C

(a) A –CH3COCH3 B –( CH3)2COMgBr C—(CH3)3COH

(b) A—CH3COOH B—(CH3)2COMgBr C—CH3CH2OH

(c) A—(CH3COO)2Ca B –CH3CH2OMgBr C—CH3-CH(OH)-CH3

Q.15 During acetylation of glucose , it needs x moles of acetic anhydride . The value of x would be :

    (a) 3                   (b) 5                   (c) 4                  (d) 1

Q. 16 Which of the following alkyl halides is hydrolysed by SN1 mechanism ?

(a) CH3Cl 

(b) CH3CH2Cl 

(c) CH3CH2CH2Cl 

(d) (CH3)3CCl

Q.17 Which of the following are the products shown by the reaction of methoxyethane with HI ?

    (a) C2H5I + CH3OH                  (b) CH3I + H2O

    (c) C2H5OH + H2O                   (d) C2H5OH + CH3I

Q.18 Denaturation of protein leads to loss of its biological activity by :

(a) formation of amino acids

(b) loss of primary structure

(c) loss of both primary and secondary structures

(d) loss of both secondary and tertiary structures

Q19 A black powder when heated with conc . HCl gives a greenish yellow gas . The gas acts as an oxidizing as well as a bleaching agent. When it is passed over slaked lime , it forms a white powder with a sickly smell , which is used as a disinfectant and is a ready source of greenish yellow gas.

The black powder and the white powder respectively are :

(a) KClO3 and NaClO3           (b) MnO2 and Ca(OCl)2

(c) MnO2 and KClO3              (d) MnCl4 and COCl2

Q20 What happens when tertiary butyl alcohol is passed over heated copper ?

(a) Sec. butyl alcohol is formed (b) 2-methylpropane is formed

(c) But-1-ene is formed             (d) Butanal is formed

ASSERTION - REASON QUESTIONS

DIRECTIONS : Question Number 21 -25 contain a statement of Assertion (A) followed by a statement of Reason (R) . Mark the correct choices as :

(a) : if both Assertion (A) and Reason (R) are true and (R) is the correct explanation of (A) .

(b) : if both (A) and (R) are true but (R) is not the correct explanation of (A) .

(c) : if (A) is true but (R) is false .

(d) : if (A) is false but (R) is true .

Q21. ASSERTION (A) : CH3- CH(Br)-CH2-CH3 on reaction with alcoholic KOH gives CH3-CH=CH-CH3 as a

result ofdehydrohalogenation .

REASON (R) ; Elimination reaction occurs in accordance with Markownikoff’s rule .

Q22. ASSERTION (A) : The specific rotation of a freshly prepared solution of alpha D- glucose decreases from + 112* to + 52.7* , while that of beta D- glucose increases from + 19* to + 52.7*.

REASON (R) : The change in specific rotation of an optically active compound with time to an equilibrium value is called Mutarotation .

Q23. ASSERTION (A) : Alpha amino acids exist as zwitterions , as they have amino and carboxylic acid groups in near vicinity .

REASON (R) : H+ ions given by – COOH group is captured by --NH2 group having a lone pair of electrons .

Q24. ASSERTION (A) : PKa value of phenol is 10.0 , while that of ethanol is 15.9 .

REASON (R) : Ethanol is stronger acid than phenol .

Q25. ASSERTION (A) : SN2 reaction of an optically active alkyl halide with aqueous KOH solution gives an alcohol with opposite sign of rotation .

REASON (R) ; SN2 reaction always proceeds with inversion of configuration .

CASE STUDY BASED QUESTIONS

CASE STUDY –1

All the elements of group 16 have ns2,np4 configuration in their outermost shell . Therefore the atoms of these elements tend to gain or share 2 electrons to achieve noble gas configuration . Sulphur and other elements of group 16 are less electronegative than oxygen , so they cannot accept electrons easily. By sharing of 2 electrons with other elements , these elements acquire ns2,np6 configuration and exhibit +2 oxidation state. Except oxygen , group 16 elements have vacant d-orbitals in their valence shell to which electrons can be promoted from s- and p- orbitals of the same shell. As a result , they can show +4 and +6 oxidation states also .

DIRECTIONS : The following questions number 26 to 30 are multiple choice questions . Choose the most appropriate answer :

Q26. Oxygen shows +2 oxidation state in :

(a) OF2 (B) H2O (C) Cl2O (d) H2O2

Q27. Like sulphur , oxygen is not able to +4 and +6 oxidation states because –

(a) oxygen is a gas while sulphur is a solid .

(b) sulphur has higher ionization enthalpy as compared to oxygen.

(c) oxygen has no d-orbitals in its valence shell .

(d) oxygen has high electron affinity as compared to sulppphur .

Q28. Compounds of sulphur with +4 oxidation state act as a/an :

(a) oxidizing agent

(b) reducing agent

(c) both oxidizing and reducing agent

(d) cannot be predicted

Q29 Oxidation state of sulphur in Na2S4O6 is :

(a) 7/2 (b) 5/2 (c) 1/2 (d) ¾

Q30. Which of the following is not a correct statement ?

(a) Oxygen molecule is paramagnetic.

(b) Sulphur shows a maximum covalency of 4.

(c) Ozone can be easily detected by mercury

(d) Both sulphurous and sulphuric acids are dibasic in nature.

CASE STUDY –2

At the freezing point of a solvent , the solid and the liquid are in equilibrium . Therefore a solution will freeze when its vapour pressure becomes equal to the vapour pressure of the pure solid solvent .

It has been observed that when a non volatile solute is added to a solvent , the freezing point of the solution is always lower than the solvent . Depression in freezing point can be given as

Del Tf = Kf .m where Kf = Molal freezing depression constant

Or we can write – del Tf = Kf.Wb. 1000 /Wa.Mb

DIRECTIONS : (Q. No 31 to 35) A statement of ASSERTION (A) followed by a statement of REASON (R) is given . Choose the correct answer out of the following choices :

(a) : (A) and (R) both are correct statements and (R) is the correct explanation of (A).

(b) : (A) and (B) both are correct statements , but (R) is not the correct explanation of (A) .

(c) : (A) is correct statement but (R) is wrong statement .

(d) : (A) is wrong statement but (R) is correct statement .

Q31. ASSERTION (A) : 0.1M solution of glucose has the same depression in freezing point as 0.1 M solution of urea.

REASON (R) : Kf for both has same value.

Q32. ASSERTION (A) : In comparation to a 0.01 M solution of benzene , the depression of freezing point of 0.01 M solution of MgCl2 is about three times .

REASON (R) : I = 3 for MgCl2 and I = 1 for benzene

Q33. ASSERTION (A) : Larger the value of cryoscopic constant of the solvent , lesser is the freezing point of the solution .

REASON (R) : Extent of depression in the freezing point is independent of the nature of the solvent .

Q34. ASSERTION (A) : The water pouch of instant cold pack for treating athletic injuries , breaks when sqeezedand NH4NO3 dissolves thus lowering the temperature .

REASON (R) : Addition of non- volatile solute into solvent depresses the freezing point of the sol vent.

Q35. ASSERTION (A) : If a non-volatile solute is mixed in a solvent , then elevation in boiling point and depression in freezing point , both will be same.

REASON (R) : Elevation in boiling point and depression in freezing point both depend on the number of particles of solute.

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