CBSE Class 12 Chemistry 2023 question paper (56/5)

Maximum marks 70 · Time 3 hours · 3 sets

Try each question first, then open its model answer. Where the paper offers a choice, both questions are shown with OR between them.

Section A

1 mark each

Q.11 mark $Which of the following molecules has a chiral centre correctly labelled with an asterisk (*) ?$
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Q.21 mark $Which of the following alcohols will not undergo oxidation ?$
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Q.31 mark $\mathrm{Sn^{2+}_{(aq)}} + 2\mathrm{e}^{-} \rightarrow \mathrm{Sn_{(s)}}$
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Q.41 mark $2\mathrm{Cl^{-}} \rightarrow \mathrm{Cl_2} + 2\mathrm{e^{-}}$
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Q.51 mark $Which property of transition metals enables them to behave as catalysts ?$
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Q.61 mark $In the two tetrahedral structures of dichromate ion$
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Q.71 mark $1 mole of liquid A and 2 moles of liquid B make a solution having a total vapour pressure 40 torr. The vapour pressure of pure A and pure B are 45 torr and 30 torr respectively. The above solution$
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Q.81 mark $Which of the following would not be a good choice for reducing nitrobenzene to aniline ?$
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Q.91 mark $(\mathrm{K_b})$
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Q.101 mark $Hydrolysis of sucrose is called$
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Q.111 mark $\mathrm{pK_a}$
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Q.121 mark $Which of the following cell was used in Apollo space programme ?$
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Q.131 mark

\mathrm{A_{(g)}} + \mathrm{B_{(g)}} \rightarrow \mathrm{C_{(g)}} + \mathrm{D_{(g)}}

Initial $[\mathrm{A_{(g)}}]$ /mol $\mathrm{dm^{-3}}$	Initial $[\mathrm{B_{(g)}}]$ /mol $\mathrm{dm^{-3}}$	Initial rate/mol $\mathrm{dm^{-3}s^{-1}}$
$3.0 \times 10^{-2}$	$2.0 \times 10^{-2}$	$1.89 \times 10^{-4}$
$3.0 \times 10^{-2}$	$4.0 \times 10^{-2}$	$1.89 \times 10^{-4}$
$6.0 \times 10^{-2}$	$4.0 \times 10^{-2}$	$7.56 \times 10^{-4}$

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Q.141 mark $\mathrm{[NiCl_4]^{2-}}$
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For questions number 15 to 18, two statements are given – one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below :
Q.151 mark $\alpha$
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Q.161 mark $Assertion (A) : For a zero order reaction the unit of rate constant and rate of reaction are same. Reason (R) : Rate of reaction for zero order reaction is independent of concentration of reactant.$
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Q.171 mark $\mathrm{Cl_2}$
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Q.181 mark $\mathrm{[Cr\,Cl_2(ox)_2]^{3-}}$
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Section B

2 marks each

Q.19 (a)2 marks $\mathrm{E^{\circ}_{Cell}}$
OR
Q.19 (b)2 marks $\mathrm{Fe_{(s)}} \mid \mathrm{Fe^{2+}}\,(0.01\mathrm{M}) \parallel \mathrm{H^{+}_{(1M)}} \mid \mathrm{H_{2(g)}}\,(1\ \mathrm{bar}),\ \mathrm{Pt_{(s)}}$
Q.202 marks $\mathrm{E_a}$
Q.212 marks $\mathrm{OH^{-}}$
Q.222 marks $Why is boiling point of o-dichlorobenzene higher than p-dichlorobenzene but melting point of para isomer is higher than ortho isomer ?$
Q.232 marks $For the pair phenol and cyclohexanol, answer the following : (a) Why is phenol more acidic than cyclohexanol ? (b) Give one chemical test to distinguish between the two.$
Q.24 (a)2 marks $-\mathrm{NH_2}$
OR
Q.24 (b)2 marks $\xrightarrow{\mathrm{CH_3CH_2OH}}$
Q.252 marks $Give the reaction of glucose with hydrogen cyanide. Presence of which group is confirmed by this reaction ?$

Section C

3 marks each

Q.263 marks $2\mathrm{N_2O_{5(g)}} \rightarrow 4\mathrm{NO_{2(g)}} + \mathrm{O_{2(g)}}$
Q.273 marks $\mathrm{d^5}$
Q.283 marks $\mathrm{(CH_3)_2NH}$
Q.293 marks $Give reasons for any 3 of the following observations : (a) Penta-acetate of glucose does not react with hydroxylamine. (b) Amino acids behave like salts. (c) Water soluble vitamins must be taken regularly in diet. (d) The two strands in DNA are complimentary to each other.$
Q.30 (a)3 marks $(i) Why is the C - O bond length in phenols less than that in methanol ? (ii) Arrange the following in order of increasing boiling point : Ethoxyethane, Butanal, Butanol, n-butane (iii) How can phenol be prepared from anisole ? Give reaction.$
OR
Q.30 (b)3 marks $\mathrm{CH_3CH_2OH} \xrightarrow[413\ \mathrm{K}]{\mathrm{H_2SO_4}} \mathrm{CH_3CH_2 - O - CH_2CH_3} + \mathrm{H_2O}$

Section D

Nucleophilic Substitution reaction of haloalkane can be conducted according to both $\mathrm{S_N}1$ and $\mathrm{S_N}2$ mechanisms. $\mathrm{S_N}1$ is a two step reaction while $\mathrm{S_N}2$ is a single step reaction. For any haloalkane which mechanism is followed depends on factors such as structure of haloalkane, properties of leaving group, nucleophilic reagent and solvent. Influences of solvent polarity : In $\mathrm{S_N}1$ reaction, the polarity of the system increases from the reactant to the transition state, because a polar solvent has a greater effect on the transition state than the reactant, thereby reducing activation energy and accelerating the reaction. In $\mathrm{S_N}2$ reaction, the polarity of the system generally does not change from the reactant to the transition state and only charge dispersion occurs. At this time, polar solvent has a great stabilizing effect on Nu than the transition state, thereby increasing activation energy and slow down the reaction rate. For example, the decomposition rate $(\mathrm{S_N}1)$ of tertiary chlorobutane at 25 °C in water (dielectric constant 79) is 300000 times faster than in ethanol (dielectric constant 24). The reaction rate $(\mathrm{S_N}2)$ of 2-Bromopropane and NaOH in ethanol containing 40% water is twice slower than in absolute ethanol. Hence the level of solvent polarity has influence on both $\mathrm{S_N}1$ and $\mathrm{S_N}2$ reaction, but with different results. Generally speaking weak polar solvent is favourable for $\mathrm{S_N}2$ reaction, while strong polar solvent is favourable for $\mathrm{S_N}1$ . Generally speaking the substitution reaction of tertiary haloalkane is based on $\mathrm{S_N}1$ mechanism in solvents with a strong polarity (for example ethanol containing water).
Q.31 (a)1 mark $\mathrm{S_N}1$
Q.31 (b)1 mark $Why is ethanol less polar than water ?$
Q.31 (c) (a)2 marks $\mathrm{S_N}2$
OR
Q.31 (c) (b)2 marks $\mathrm{S_N}1$

Rahul set-up an experiment to find resistance of aqueous KCl solution for different concentrations at 298 K using a conductivity cell connected to a Wheatstone bridge. He fed the Wheatstone bridge with a.c. power in the audio frequency range 550 to 5000 cycles per second. Once the resistance was calculated from null point he also calculated the conductivity K and molar conductivity

\Lambda_{\mathrm{m}}

and recorded his readings in tabular form.

S.No.	Conc.(M)	k S $\mathrm{cm^{-1}}$	$\Lambda_{\mathrm{m}}$ S $\mathrm{cm^2\ mol^{-1}}$
1.	1.00	$111.3 \times 10^{-3}$	111.3
2.	0.10	$12.9 \times 10^{-3}$	129.0
3.	0.01	$1.41 \times 10^{-3}$	141.0

Q.32 (a)1 mark

Why does conductivity decrease with dilution ?

Q.32 (b)1 mark $\Lambda_{\mathrm{m}}^{\circ}$
Q.32 (c) (a)2 marks $\Lambda_{\mathrm{m}}$
OR
Q.32 (c) (b)2 marks $\mathrm{CH_3COOH}$

Section E

5 marks each

Q.33 (a)5 marks $\mathrm{mol^{-1}}$
OR
Q.33 (b)5 marks $2.32 \times 10^{-2}$
Q.34 (a)5 marks $\mathrm{C_5H_8O_2}$
OR
Q.34 (b)5 marks $\alpha$
Q.355 marks $3\,\mathrm{MnO_4^{2-}} + 4\mathrm{H^{+}} \rightarrow$

Section A

1 mark each

Q.11 mark $\mathrm{pK_a}$
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Q.21 mark $Which of the following cell was used in Apollo space programme ?$
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Q.31 mark $\mathrm{Fe^{3+}_{(aq)}} + \mathrm{e}^{-} \rightarrow \mathrm{Fe^{2+}_{(aq)}}$
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Q.41 mark

\mathrm{A_{(g)}} + \mathrm{B_{(g)}} \rightarrow \mathrm{C_{(g)}} + \mathrm{D_{(g)}}

Initial $[\mathrm{A_{(g)}}]$ /mol $\mathrm{dm^{-3}}$	Initial $[\mathrm{B_{(g)}}]$ /mol $\mathrm{dm^{-3}}$	Initial rate/mol $\mathrm{dm^{-3}s^{-1}}$
$3.0 \times 10^{-2}$	$2.0 \times 10^{-2}$	$1.89 \times 10^{-4}$
$3.0 \times 10^{-2}$	$4.0 \times 10^{-2}$	$1.89 \times 10^{-4}$
$6.0 \times 10^{-2}$	$4.0 \times 10^{-2}$	$7.56 \times 10^{-4}$

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Q.51 mark $\mathrm{[NiCl_4]^{2-}}$
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Q.61 mark $\mathrm{3d^6}$
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Q.71 mark $Which of the following aqueous solution will have highest boiling point ?$
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Q.81 mark $\mathrm{Sn^{2+}_{(aq)}} + 2\mathrm{e}^{-} \rightarrow \mathrm{Sn_{(s)}}$
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Q.91 mark $Amides can be converted into amines by the reaction named$
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Q.101 mark $Which of the following statements is not true about glucose ?$
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Q.111 mark $Which of the following alcohols will not undergo oxidation ?$
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Q.121 mark $2\mathrm{Cl^{-}} \rightarrow \mathrm{Cl_2} + 2\mathrm{e^{-}}$
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Q.131 mark $Which property of transition metals enables them to behave as catalysts ?$
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Q.141 mark $Which of the following would not be a good choice for reducing nitrobenzene to aniline ?$
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For questions number 15 to 18, two statements are given – one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below :
Q.151 mark $Assertion (A) : Vitamin C cannot be stored in our body. Reason (R) : Vitamin C is fat soluble and is excreted from the body in urine.$
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Q.161 mark $Assertion (A) : The half life of a reaction is the time in which the concentration of the reactant is reduced to one half of its initial concentration. Reason (R) : In first order kinetics when concentration of reactant is doubled, its half life is doubled.$
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Q.171 mark $Assertion (A) : Bromination of benzoic acid gives m-bromobenzoic acid. Reason (R) : Carboxyl group increases the electron density at the meta position.$
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Q.181 mark $Assertion (A) : EDTA is a hexadentate ligand. Reason (R) : EDTA has 2 nitrogen and 4 oxygen donor atoms.$
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Section B

2 marks each

Q.192 marks $\mathrm{OH^{-}}$
Q.202 marks $For the pair phenol and cyclohexanol, answer the following : (a) Why is phenol more acidic than cyclohexanol ? (b) Give one chemical test to distinguish between the two.$
Q.21 (a)2 marks $-\mathrm{NH_2}$
OR
Q.21 (b)2 marks $\xrightarrow{\mathrm{CH_3CH_2OH}}$
Q.222 marks $\mathrm{CH_3Cl}$
Q.232 marks $\mathrm{E_a}$
Q.24 (a)2 marks $\mathrm{E^{\circ}_{Cell}}$
OR
Q.24 (b)2 marks $\mathrm{Fe_{(s)}} \mid \mathrm{Fe^{2+}}\,(0.01\mathrm{M}) \parallel \mathrm{H^{+}_{(1M)}} \mid \mathrm{H_{2(g)}}\,(1\ \mathrm{bar}),\ \mathrm{Pt_{(s)}}$
Q.252 marks $Give the reaction of glucose with acetic anhydride. Presence of which group is confirmed by this reaction ?$

Section C

3 marks each

Q.26 (a)3 marks $(i) Why is the C - O bond length in phenols less than that in methanol ? (ii) Arrange the following in order of increasing boiling point : Ethoxyethane, Butanal, Butanol, n-butane (iii) How can phenol be prepared from anisole ? Give reaction.$
OR
Q.26 (b)3 marks $\mathrm{CH_3CH_2OH} \xrightarrow[413\ \mathrm{K}]{\mathrm{H_2SO_4}} \mathrm{CH_3CH_2 - O - CH_2CH_3} + \mathrm{H_2O}$
Q.273 marks $\mathrm{d^5}$
Q.283 marks $Give reasons for any 3 of the following observations : (a) Penta-acetate of glucose does not react with hydroxylamine. (b) Amino acids behave like salts. (c) Water soluble vitamins must be taken regularly in diet. (d) The two strands in DNA are complimentary to each other.$
Q.293 marks $2\mathrm{N_2O_{5(g)}} \rightarrow 4\mathrm{NO_{2(g)}} + \mathrm{O_{2(g)}}$
Q.303 marks $\mathrm{(CH_3)_2NH}$

Section D

\Lambda_{\mathrm{m}}

and recorded his readings in tabular form.

S.No.	Conc.(M)	k S $\mathrm{cm^{-1}}$	$\Lambda_{\mathrm{m}}$ S $\mathrm{cm^2\ mol^{-1}}$
1.	1.00	$111.3 \times 10^{-3}$	111.3
2.	0.10	$12.9 \times 10^{-3}$	129.0
3.	0.01	$1.41 \times 10^{-3}$	141.0

Q.31 (a)1 mark

Why does conductivity decrease with dilution ?

Q.31 (b)1 mark $\Lambda_{\mathrm{m}}^{\circ}$
Q.31 (c) (a)2 marks $\Lambda_{\mathrm{m}}$
OR
Q.31 (c) (b)2 marks $\mathrm{CH_3COOH}$
Nucleophilic Substitution reaction of haloalkane can be conducted according to both $\mathrm{S_N}1$ and $\mathrm{S_N}2$ mechanisms. $\mathrm{S_N}1$ is a two step reaction while $\mathrm{S_N}2$ is a single step reaction. For any haloalkane which mechanism is followed depends on factors such as structure of haloalkane, properties of leaving group, nucleophilic reagent and solvent. Influences of solvent polarity : In $\mathrm{S_N}1$ reaction, the polarity of the system increases from the reactant to the transition state, because a polar solvent has a greater effect on the transition state than the reactant, thereby reducing activation energy and accelerating the reaction. In $\mathrm{S_N}2$ reaction, the polarity of the system generally does not change from the reactant to the transition state and only charge dispersion occurs. At this time, polar solvent has a great stabilizing effect on Nu than the transition state, thereby increasing activation energy and slow down the reaction rate. For example, the decomposition rate $(\mathrm{S_N}1)$ of tertiary chlorobutane at 25 °C in water (dielectric constant 79) is 300000 times faster than in ethanol (dielectric constant 24). The reaction rate $(\mathrm{S_N}2)$ of 2-Bromopropane and NaOH in ethanol containing 40% water is twice slower than in absolute ethanol. Hence the level of solvent polarity has influence on both $\mathrm{S_N}1$ and $\mathrm{S_N}2$ reaction, but with different results. Generally speaking weak polar solvent is favourable for $\mathrm{S_N}2$ reaction, while strong polar solvent is favourable for $\mathrm{S_N}1$ . Generally speaking the substitution reaction of tertiary haloalkane is based on $\mathrm{S_N}1$ mechanism in solvents with a strong polarity (for example ethanol containing water).
Q.32 (a)1 mark $\mathrm{S_N}1$
Q.32 (b)1 mark $Why is ethanol less polar than water ?$
Q.32 (c) (a)2 marks $\mathrm{S_N}2$
OR
Q.32 (c) (b)2 marks $\mathrm{S_N}1$

Section E

5 marks each

Q.33 (a)5 marks $\mathrm{C_5H_8O_2}$
OR
Q.33 (b)5 marks $\alpha$
Q.34 (a)5 marks $\mathrm{mol^{-1}}$
OR
Q.34 (b)5 marks $2.32 \times 10^{-2}$
Q.355 marks $\mathrm{4s^2\ 3d^3}$

Section A

1 mark each

Q.11 mark $\mathrm{[NiCl_4]^{2-}}$
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Q.21 mark

\mathrm{A_{(g)}} + \mathrm{B_{(g)}} \rightarrow \mathrm{C_{(g)}} + \mathrm{D_{(g)}}

Initial $[\mathrm{A_{(g)}}]$ /mol $\mathrm{dm^{-3}}$	Initial $[\mathrm{B_{(g)}}]$ /mol $\mathrm{dm^{-3}}$	Initial rate/mol $\mathrm{dm^{-3}s^{-1}}$
$3.0 \times 10^{-2}$	$2.0 \times 10^{-2}$	$1.89 \times 10^{-4}$
$3.0 \times 10^{-2}$	$4.0 \times 10^{-2}$	$1.89 \times 10^{-4}$
$6.0 \times 10^{-2}$	$4.0 \times 10^{-2}$	$7.56 \times 10^{-4}$

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Q.31 mark $\mathrm{Sn^{2+}_{(aq)}} + 2\mathrm{e^{-}} \rightarrow \mathrm{Sn_{(s)}}$
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Q.41 mark $Which of the following cell was used in Apollo space programme ?$
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Q.51 mark $Which of the following alcohols will not undergo oxidation ?$
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Q.61 mark $The unit of molar conductivity is$
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Q.71 mark $Out of the following 1.0 M aqueous solutions, which one will show largest freezing point depression ?$
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Q.81 mark $Which of the following molecules has a chiral centre correctly labelled with an asterisk (*) ?$
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Q.91 mark $\mathrm{C_6H_5NH_2} + \mathrm{CHCl_3} + 3\ \mathrm{KOH} \rightarrow \mathrm{A} + 3\mathrm{B} + 3\mathrm{C}$
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Q.101 mark $\beta$
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Q.111 mark $2\mathrm{Cl^{-}} \rightarrow \mathrm{Cl_2} + 2\mathrm{e^{-}}$
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Q.121 mark $Which property of transition metals enables them to behave as catalysts ?$
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Q.131 mark $Which of the following would not be a good choice for reducing nitrobenzene to aniline ?$
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Q.141 mark $\mathrm{pK_a}$
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For questions number 15 to 18, two statements are given – one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below :
Q.151 mark $Assertion (A) : The backbone of DNA and RNA molecules is a chain consisting of heterocyclic base, pentose sugar and phosphate group. Reason (R) : Nucleotides and nucleosides mainly differ from each other in presence of phosphate group.$
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Q.161 mark $Assertion (A) : Order of reaction is applicable to elementary as well as complex reactions. Reason (R) : For a complex reaction molecularity has no meaning.$
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Q.171 mark $\alpha$
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Q.181 mark $\mathrm{[Co(NH_3)_5\ SO_4]}\ \mathrm{Cl}$
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Section B

2 marks each

Q.192 marks $For the pair phenol and cyclohexanol, answer the following : (a) Why is phenol more acidic than cyclohexanol ? (b) Give one chemical test to distinguish between the two.$
Q.202 marks $\mathrm{OH^{-}}$
Q.212 marks $\mathrm{E_a}$
Q.222 marks $Why haloarenes are not reactive towards nucleophilic substitution reaction ? Give two reasons.$
Q.23 (a)2 marks $\mathrm{E^{\circ}_{Cell}}$
OR
Q.23 (b)2 marks $\mathrm{Fe_{(s)}} \mid \mathrm{Fe^{2+}}\,(0.01\mathrm{M}) \parallel \mathrm{H^{+}_{(1M)}} \mid \mathrm{H_{2(g)}}\,(1\ \mathrm{bar}),\ \mathrm{Pt_{(s)}}$
Q.24 (a)2 marks $-\mathrm{NH_2}$
OR
Q.24 (b)2 marks $\xrightarrow{\mathrm{CH_3CH_2OH}}$
Q.252 marks $Give the reaction of heating glucose with hydroxylamine. Presence of which group is confirmed by this reaction ?$

Section C

3 marks each

Q.263 marks $Give reasons for any 3 of the following observations : (a) Penta-acetate of glucose does not react with hydroxylamine. (b) Amino acids behave like salts. (c) Water soluble vitamins must be taken regularly in diet. (d) The two strands in DNA are complimentary to each other.$
Q.273 marks $\mathrm{d^4}$
Q.28 (a)3 marks $(i) Why is the C - O bond length in phenols less than that in methanol ? (ii) Arrange the following in order of increasing boiling point : Ethoxyethane, Butanal, Butanol, n-butane (iii) How can phenol be prepared from anisole ? Give reaction.$
OR
Q.28 (b)3 marks $\mathrm{CH_3CH_2OH} \xrightarrow[413\ \mathrm{K}]{\mathrm{H_2SO_4}} \mathrm{CH_3CH_2 - O - CH_2CH_3} + \mathrm{H_2O}$
Q.293 marks $\mathrm{(CH_3)_2NH}$
Q.303 marks $2\mathrm{N_2O_{5(g)}} \rightarrow 4\mathrm{NO_{2(g)}} + \mathrm{O_{2(g)}}$

Section D

Nucleophilic Substitution reaction of haloalkane can be conducted according to both $\mathrm{S_N}1$ and $\mathrm{S_N}2$ mechanisms. $\mathrm{S_N}1$ is a two step reaction while $\mathrm{S_N}2$ is a single step reaction. For any haloalkane which mechanism is followed depends on factors such as structure of haloalkane, properties of leaving group, nucleophilic reagent and solvent. Influences of solvent polarity : In $\mathrm{S_N}1$ reaction, the polarity of the system increases from the reactant to the transition state, because a polar solvent has a greater effect on the transition state than the reactant, thereby reducing activation energy and accelerating the reaction. In $\mathrm{S_N}2$ reaction, the polarity of the system generally does not change from the reactant to the transition state and only charge dispersion occurs. At this time, polar solvent has a great stabilizing effect on Nu than the transition state, thereby increasing activation energy and slow down the reaction rate. For example, the decomposition rate $(\mathrm{S_N}1)$ of tertiary chlorobutane at 25 °C in water (dielectric constant 79) is 300000 times faster than in ethanol (dielectric constant 24). The reaction rate $(\mathrm{S_N}2)$ of 2-Bromopropane and NaOH in ethanol containing 40% water is twice slower than in absolute ethanol. Hence the level of solvent polarity has influence on both $\mathrm{S_N}1$ and $\mathrm{S_N}2$ reaction, but with different results. Generally speaking weak polar solvent is favourable for $\mathrm{S_N}2$ reaction, while strong polar solvent is favourable for $\mathrm{S_N}1$ . Generally speaking the substitution reaction of tertiary haloalkane is based on $\mathrm{S_N}1$ mechanism in solvents with a strong polarity (for example ethanol containing water).
Q.31 (a)1 mark $\mathrm{S_N}1$
Q.31 (b)1 mark $Why is ethanol less polar than water ?$
Q.31 (c) (a)2 marks $\mathrm{S_N}2$
OR
Q.31 (c) (b)2 marks $\mathrm{S_N}1$

\Lambda_{\mathrm{m}}

and recorded his readings in tabular form.

S.No.	Conc.(M)	k S $\mathrm{cm^{-1}}$	$\Lambda_{\mathrm{m}}$ S $\mathrm{cm^2\ mol^{-1}}$
1.	1.00	$111.3 \times 10^{-3}$	111.3
2.	0.10	$12.9 \times 10^{-3}$	129.0
3.	0.01	$1.41 \times 10^{-3}$	141.0

Q.32 (a)1 mark

Why does conductivity increase though the conductivity decrease with dilution ?

Q.32 (b)1 mark $\Lambda_{\mathrm{m}}^{\circ}$
Q.32 (c) (a)2 marks $\Lambda_{\mathrm{m}}$
OR
Q.32 (c) (b)2 marks $\mathrm{CH_3COOH}$

Section E

5 marks each

Q.33 (a)5 marks $\mathrm{C_5H_8O_2}$
OR
Q.33 (b)5 marks $\alpha$
Q.34 (a)5 marks $\mathrm{mol^{-1}}$
OR
Q.34 (b)5 marks $2.32 \times 10^{-2}$
Q.355 marks $\mathrm{Cr^{3+}}$