Most Important Questions For Class 12th CBSE

Most Important Questions of All The Chaptar of Class 12th Below are the important questions along with the answers .These questions are most asked in the recent school exams. These are totally based on the CBSE board curriculum. We recommend everyone, do not skip these questions.

Important Questions of All The Chaptar of Class 12th

Solution

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1 Which of the following solutions will have the highest conductivity at 298 K 298 K 298K298 \mathrm{~K}298 K ?
(a) 0.01 M H C l 0.01 M H C l 0.01MHCl0.01 \mathrm{MHCl}0.01MHCl solution
(b) 0.1 M H C l 0.1 M H C l 0.1MHCl0.1 \mathrm{MHCl}0.1MHCl solution
(c) 0.01 M C H 3 C O O H 0.01 M C H 3 C O O H 0.01MCH_(3)COOH0.01 \mathrm{MCH}_3 \mathrm{COOH}0.01MCH3COOH solution
(d) 0.1 M C H 3 C O O H 0.1 M C H 3 C O O H 0.1MCH_(3)COOH0.1 \mathrm{MCH}_3 \mathrm{COOH}0.1MCH3COOH solution
2 A 5 % 5 % 5%5 \%5% solution of N a 2 S O 4 ⋅ 1 H 2 O ( M W = 322 ) N a 2 S O 4 ⋅ 1 H 2 O ( M W = 322 ) Na_(2)SO_(4)*1H_(2)O(MW=322)\mathrm{Na}_2 \mathrm{SO}_4 \cdot 1 \mathrm{H}_2 \mathrm{O}(\mathrm{MW}=322)Na2SO4⋅1H2O(MW=322) is isotonic with 2 % 2 % 2%2 \%2% solution of non- electrolytic, non volatile substance X X XXX. Find out the molecular weight of X X XXX.
3 Answer the following questions:
a. State Henry's law and explain why are the tanks used by scuba divers filled with air diluted with helium ( 11.7 % 11.7 % 11.7%11.7 \%11.7% helium, 56.2 % 56.2 % 56.2%56.2 \%56.2% nitrogen and 32.1 % 32.1 % 32.1%32.1 \%32.1% oxygen)?
b. Assume that argon exerts a partial pressure of 6 bar. Calculate the solubility of argon gas in water.
(Given Henry's law constant for argon dissolved in water, K H = 40 k b a r K H = 40 k b a r K_(H)=40kbar\mathrm{K}_{\mathrm{H}}=40 \mathrm{kbar}KH=40kbar )

Electrochemistry

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  1. Given below are two statements labelled as Assertion (A) and Reason (R)
    Assertion (A): During electrolysis of aqueous copper sulphate solution using copper electrodes hydrogen gas is released at the cathode.
    Reason (R): The electrode potential of C u 2 + / C u C u 2 + / C u Cu^(2+)//Cu\mathrm{Cu}^{2+} / \mathrm{Cu}Cu2+/Cu is greater than that of H + / H 2 H + / H 2 H+//H_(2)\mathrm{H}+/ \mathrm{H}_2H+/H2
    Select the most appropriate answer from the options given below:
    (a) Both A A AAA and R R RRR are true and R R RRR is the correct explanation of A A AAA
    (b) Both A A AAA and R R RRR are true but R R RRR is not the correct explanation of A A AAA.
    (c) A A AAA is true but R R RRR is false.
    (d) A A AAA is false but R R RRR is true.
  2. (a) Can we construct an electrochemical cell with two half-cells composed of Z n S O 4 Z n S O 4 ZnSO_(4)\mathrm{ZnSO}_4ZnSO4 solution and zinc electrodes? Explain your answer.
    (b) Calculate the λ 0 m λ 0 m lambda^(0)m\lambda^0 \mathrm{~m}λ0 m for C l C l Cl\mathrm{Cl}Cl - ion from the data given below:
Λ 0 m M g C l 2 = 258.6 S c m 2 m o l − 1 and λ 0 m M g 2 + = 106 S c m 2 m o l − 1 Λ 0 m M g C l 2 = 258.6 S c m 2 m o l − 1  and  λ 0 m M g 2 + = 106 S c m 2 m o l − 1 Lambda^(0)mMgCl2=258.6Scm^(2)mol^(-1)" and "lambda^(0)mMg^(2+)=106Scm^(2)mol^(-1)\Lambda^0 \mathrm{mMgCl} 2=258.6 \mathrm{Scm}^2 \mathrm{~mol}^{-1} \text { and } \lambda^0 \mathrm{mMg}^{2+}=106 \mathrm{Scm}^2 \mathrm{~mol}^{-1}Λ0mMgCl2=258.6Scm2 mol−1 and λ0mMg2+=106Scm2 mol−1
(c) The cell constant of a conductivity cell is 0.146 c m − 1 0.146 c m − 1 0.146cm^(-1)0.146 \mathrm{~cm}^{-1}0.146 cm−1. What is the conductivity of 0.01 M 0.01 M 0.01M0.01 \mathrm{M}0.01M solution of an electrolyte at 298 K 298 K 298K298 \mathrm{~K}298 K, if the resistance of the cell is 1000 o h m 1000 o h m 1000ohm1000 \mathrm{ohm}1000ohm ?
3. The molar conductivity of C H 3 C O O H C H 3 C O O H CH_(3)COOH\mathrm{CH}_3 \mathrm{COOH}CH3COOH at infinite dilution is 390 S c m 2 / m o l 390 S c m 2 / m o l 390Scm^(2)//mol390 \mathrm{Scm}^2 / \mathrm{mol}390Scm2/mol. Using the graph and given information, the molar conductivity of C H 3 C O O K C H 3 C O O K CH_(3)COOK\mathrm{CH}_3 \mathrm{COOK}CH3COOK will be:
a. 100 S c m 2 / m o l 100 S c m 2 / m o l 100Scm^(2)//mol100 \mathrm{Scm}^2 / \mathrm{mol}100Scm2/mol
b. 115 S c m 2 / m o l 115 S c m 2 / m o l 115Scm^(2)//mol115 \mathrm{Scm}^2 / \mathrm{mol}115Scm2/mol
c. 150 S c m 2 / m o l 150 S c m 2 / m o l 150Scm^(2)//mol150 \mathrm{Scm}^2 / \mathrm{mol}150Scm2/mol
d. 125 S c m 2 / m o l 125 S c m 2 / m o l 125Scm^(2)//mol125 \mathrm{Scm}^2 / \mathrm{mol}125Scm2/mol
math

Chemical Kinetics

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1 Which of the following statement is true?
(a) molecularity of reaction can be zero or a fraction.
(b) molecularity has no meaning for complex reactions.
(c) molecularity of a reaction is an experimental quantity
(d) reactions with the molecularity three are very rare but are fast.
2 If the initial concentration of substance A A AAA is 1.5 M 1.5 M 1.5M1.5 \mathrm{M}1.5M and after 120 seconds the concentration of substance A A AAA is 0.75 M 0.75 M 0.75M0.75 \mathrm{M}0.75M, the rate constant for the reaction if it follows zero - order kinetics is:
(a) 0.00625 m o l L − 1 s − 1 0.00625 m o l L − 1 s − 1 0.00625molL^(-1)s^(-1)0.00625 \mathrm{molL}^{-1} \mathrm{~s}^{-1}0.00625molL−1 s−1
(b) 0.00625 s − 1 0.00625 s − 1 0.00625s^(-1)0.00625 \mathrm{~s}^{-1}0.00625 s−1
(c) 0.00578 m o l L − 1 s − 1 0.00578 m o l L − 1 s − 1 0.00578molL^(-1)s^(-1)0.00578 \mathrm{molL}^{-1} \mathrm{~s}^{-1}0.00578molL−1 s−1
(d) 0.00578 s − 1 0.00578 s − 1 0.00578s^(-1)0.00578 \mathrm{~s}^{-1}0.00578 s−1
3 a. Radioactive decay follows first - order kinetics. The initial amount of two radioactive elements X X XXX and Y Y YYY is 1 g m 1 g m 1gm1 \mathrm{gm}1gm each. What will be the ratio of X X XXX and Y Y YYY after two days if their halflives are 12 hours and 16 hours respectively?
b. The hypothetical reaction P + Q → R P + Q → R P+Q rarr RP+Q \rightarrow RP+Q→R is half order w.r.t ' P P PPP ' and zero order w.r.t ' Q Q QQQ '. What is the unit of rate constant for this reaction?

D and F block

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1 Match the properties with the elements of 3 d 3 d 3d3 d3d series:
(i) lowest enthalpy of atomization
(p) Sc
(ii) shows maximum number of oxidation states
(q) M n M n Mn\mathrm{Mn}Mn
(iii) transition metal that does not form coloured compounds
(r) Z n Z n Zn\mathrm{Zn}Zn
(s) T i T i Ti\mathrm{Ti}Ti
(a) (i) (r), (ii) (q), (iii) (p)
(b) (i) (r), (ii) (s), (iii) (p)
(c) (i) (p), (ii) (q), (iii) (r)
(d) (i) (s), (ii) (r), (iii) (p)
2 The trend of which property is represented by the following graph?
(a) ionization enthalpy
(b) atomic radii
(c) enthalpy of atomization
(d) melting point
3 Which of the following is not considered a transition element?
(a) Scandium
(b) Silver
(c) Vanadium
(d) Zinc
d and f

Coordination Compounds

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1 (a) Write the formula for the following coordination compound
Bis(ethane-1,2-diamine) dihydroxidochromium(III) chloride
(b) Does ionization isomer for the following compound exist? Justify your answer. H g [ C o ( S C N ) 4 ] H g C o ( S C N ) 4 Hg[Co(SCN)_(4)]\mathrm{Hg}\left[\mathrm{Co}(\mathrm{SCN})_4\right]Hg[Co(SCN)4]
(c) Is the central metal atom in coordination complexes a Lewis acid or a Lewis base? Explain.
2 The CFSE of [ C o C l 6 ] 3 − C o C l 6 3 − [CoCl_(6)]^(3-)\left[\mathrm{CoCl}_6\right]^{3-}[CoCl6]3− is 18000 c m − 1 18000 c m − 1 18000cm^(-1)18000 \mathrm{~cm}^{-1}18000 cm−1 the CFSE for [ C o C l 4 ] − C o C l 4 − [CoCl_(4)]^(-)\left[\mathrm{CoCl}_4\right]^{-}[CoCl4]−will be:
a. 18000 c m − 1 18000 c m − 1 18000cm^(-1)18000 \mathrm{~cm}^{-1}18000 cm−1
b. 8000 c m − 1 8000 c m − 1 8000cm^(-1)8000 \mathrm{~cm}^{-1}8000 cm−1
c. 2000 c m − 1 2000 c m − 1 2000cm^(-1)2000 \mathrm{~cm}^{-1}2000 cm−1
d. 16000 c m − 1 16000 c m − 1 16000cm^(-1)16000 \mathrm{~cm}^{-1}16000 cm−1
3 The number of ions formed on dissolving one molecule of F e S O 4 ⋅ ( N H 4 ) 2 S O 4 ⋅ 6 H 2 C F e S O 4 ⋅ N H 4 2 S O 4 ⋅ 6 H 2 C FeSO_(4)*(NH_(4))_(2)SO_(4)*6H_(2)C\mathrm{FeSO}_4 \cdot\left(\mathrm{NH}_4\right)_2 \mathrm{SO}_4 \cdot 6 \mathrm{H}_2 \mathrm{C}FeSO4⋅(NH4)2SO4⋅6H2C in water is:
a. 3
b. 4
c. 5
d. 6

Haloalkanes and Haloarenes

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1 (a) Arrange the isomeric dichlorobenzene in the increasing order of their boiling point and melting points.
(b) Explain why the electrophilic substitution reactions in haloarenes occur slowly and require more drastic conditions as compared to those in benzene.
2 Which one of the following compounds is more reactive towards S N 1 S N 1 S_(N)1\mathrm{S}_{\mathrm{N}} 1SN1 reaction?
a. C H 2 = C H C H 2 B r C H 2 = C H C H 2 B r CH_(2)=CHCH_(2)Br\mathrm{CH}_2=\mathrm{CHCH}_2 \mathrm{Br}CH2=CHCH2Br
b. C 6 H 5 C H 2 B r C 6 H 5 C H 2 B r C_(6)H_(5)CH_(2)Br\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{Br}C6H5CH2Br
c. C 6 H 5 C H ( C 6 H 5 ) B r C 6 H 5 C H C 6 H 5 B r C_(6)H_(5)CH(C_(6)H_(5))Br\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}\left(\mathrm{C}_6 \mathrm{H}_5\right) \mathrm{Br}C6H5CH(C6H5)Br
d. C 6 H 5 C H ( C H 3 ) B r C 6 H 5 C H C H 3 B r C_(6)H_(5)CH(CH_(3))Br\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}\left(\mathrm{CH}_3\right) \mathrm{Br}C6H5CH(CH3)Br
3 What would be the major product of the following reaction?
C 6 H 5 − C H 2 − O C 6 H 5 + H B r → A + B C 6 H 5 − C H 2 − O C 6 H 5 + H B r → A + B C_(6)H_(5)-CH_(2)-OC_(6)H5+HBrrarrA+B\mathrm{C}_6 \mathrm{H}_5-\mathrm{CH}_2-\mathrm{OC}_6 \mathrm{H} 5+\mathrm{HBr} \rightarrow \mathrm{A}+\mathrm{B}C6H5−CH2−OC6H5+HBr→A+B
a. A = C 6 H 5 C H 2 O H , B = C 6 H 6 A = C 6 H 5 C H 2 O H , B = C 6 H 6 A=C_(6)H_(5)CH_(2)OH,B=C_(6)H_(6)\mathrm{A}=\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{OH}, \mathrm{B}=\mathrm{C}_6 \mathrm{H}_6A=C6H5CH2OH,B=C6H6
b. A = C 6 H 5 C H 2 O H , B = C 6 H 5 B r A = C 6 H 5 C H 2 O H , B = C 6 H 5 B r A=C_(6)H_(5)CH_(2)OH,B=C6H5Br\mathrm{A}=\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{OH}, \mathrm{B}=\mathrm{C} 6 \mathrm{H} 5 \mathrm{Br}A=C6H5CH2OH,B=C6H5Br
c. A = C 6 H 5 C H 3 , B = C 6 H 5 B r A = C 6 H 5 C H 3 , B = C 6 H 5 B r A=C_(6)H_(5)CH_(3),B=C_(6)H_(5)Br\mathrm{A}=\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_3, \mathrm{~B}=\mathrm{C}_6 \mathrm{H}_5 \mathrm{Br}A=C6H5CH3, B=C6H5Br
d. A = C 6 H 5 C H 2 B r , B = C 6 H 5 O H A = C 6 H 5 C H 2 B r , B = C 6 H 5 O H A=C_(6)H_(5)CH_(2)Br,B=C_(6)H_(5)OHA=C_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{Br}, \mathrm{B}=\mathrm{C}_6 \mathrm{H}_5 \mathrm{OH}A=C6H5CH2Br,B=C6H5OH

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