Chemistry Board Sample Paper 2024-2025 Science (English Medium) Class 12 Question Paper Solution

Ammonolysis of ethyl chloride followed by reaction of the amine so formed with 1 mole of methyl chloride gives an amine that ______.

reacts with Hinsberg reagent to form a product soluble in an alkali.

on reaction with Nitrous acid, produced nitrogen gas.

reacts with Benzenesulphonyl chloride to form a product that is insoluble in alkali.

does not react with Hinsberg reagent.

Which one of the following has the highest dipole moment?

\[\ce{CH3F}\]

\[\ce{CH3Cl}\]

\[\ce{CH3I}\]

\[\ce{CH3Br}\]

Match the properties given in column I with the metals in column II:

(i) - (C), (ii) - (B), (iii) - (A)

(i) - (C), (ii) - (A), (iii) - (B)

(i) - (A), (ii) - (B), (iii) - (C)

(i) - (B), (ii) - (A), (iii) - (C)

Study the graph showing the boiling points of bromoalkanes and identify the compounds.

1 = Bromomethane, 2 = 2-Bromobutane, 3 = 1-Bromobutane, 4 = 2-Bromo-2-methylpropane 

1 = 1-Bromobutane, 2 = 2-Bromo-2-methylpropane, 3 = 2-Bromobutane, 4 = Bromomethane

1 = Bromomethane, 2 = 1-Bromobutane, 3 = 2-Bromo-2-methylpropane, 4 = 2-Bromobutane

1 = Bromomethane, 2 = 2-Bromo-2-methylpropane, 3 = 2-Bromobutane, 4 = 1-Bromobutane

The initial concentration of R in the reaction \[\ce{R -> P}\] is 4.62 × 10^-2 mol/L. What is the half life for the reaction if k = 2.31 × 10^-2 mol L^-1 s^-1?

30 s

3 s

1 s

10 s

When \[\ce{C6H5COOCOCH3}\] is treated with \[\ce{H2O}\], the product obtained is ______.

Benzoic acid and ethanol

Benzoic acid and ethanoic acid

Acetic Acid and phenol

Benzoic anhydride and methanol

‘X’ and ‘Y’ in the above table are:

X = \[\ce{[Co(NH3)6]^{2+} 3Cl−}\], Y = 1 : 3

X = \[\ce{[Co(NH3)4Cl2]+Cl-}\], Y = 1 : 3

X = \[\ce{[Co(NH3)4Cl2]+Cl−}\], Y = 1 : 1

X = \[\ce{[Co(NH3)4Cl2]^{3+} 3Cl−}\], Y = 1 : 1

Which of the following contains only β-D-glucose as its monosaccharide unit?

Sucrose

Cellulose

Starch

Maltose

Which one of the following sets correctly represents the increase in the paramagnetic property of the ions?

\[\ce{Ti^{3+} < Fe^{2+} < Cr^{3+} < Mn^{2+}}\]

\[\ce{Ti^{3+} < Mn^{2+} < Fe^{2+} < Cr^{3+}}\]

\[\ce{Mn^{2+} < Fe^{2+} < Cr^{3+} < Ti^{3+}}\]

\[\ce{Ti^{3+} < Cr^{3+} < Fe^{2+} < Mn^{2+}}\]

A first-order reaction is found to have a rate constant, k = 5.5 × 10^-14 s^-1. The time taken for completion of the reaction is:

1.26 × 10¹³ s

2.52 × 10¹³ s

0.63 × 10¹³ s

It never goes to completion.

A student was preparing aniline in the lab. She took a compound “X” and reduced it in the presence of Ni as a catalyst. What could be the compound “X”?

Nitrobenzene

1-Nitrohexane

Benzonitrile

1-Hexanenitrile

Which of the following compound gives an oxime with hydroxylamine:

\[\ce{CH3COCH3}\]

\[\ce{CH3COOH}\]

\[\ce{(CH3CO)2O}\]

\[\ce{CH3COCl}\]

Assertion (A): \[\ce{[Mn(CN)6]^{3−}}\] has a magnetic moment of two unpaired electrons while \[\ce{[MnCl6]^{3−}}\] has a paramagnetic moment of four unpaired electrons.

Reason (R): \[\ce{[Mn(CN)6]^{3−}}\] is an inner orbital complex involving d²sp³ hybridisation; on the other hand, \[\ce{[MnCl6]^{3−}}\] is an outer orbital complex involving sp³d² hybridisation.

Select the most appropriate answer from the options given below:

Both A and R are true and R is the correct explanation of A.

Both A and R are true but R is not the correct explanation of A.

A is true but R is false.

A is false but R is true.

Assertion (A): For strong electrolytes, there is a slow increase in molar conductivity with dilution and can be represented by the equation
`wedge_m^circ = wedge_m - A  c^(1//2)`

Reason (R): The value of the constant ‘A’ for \[\ce{NaCl}\], \[\ce{CaCl2}\], and \[\ce{MgSO4}\] in a given solvent and at a given temperature is different.

Select the most appropriate answer from the options given below:

Both A and R are true and R is the correct explanation of A.

Both A and R are true but R is not the correct explanation of A.

A is true but R is false.

A is false but R is true.

Assertion (A): Glucose does not form the hydrogensulphite addition product with \[\ce{NaHSO3}\].

Reason (R): Glucose exists in a six-membered cyclic structure called the pyranose structure.

Select the most appropriate answer from the options given below:

Both A and R are true and R is the correct explanation of A.

Both A and R are true but R is not the correct explanation of A.

A is true but R is false.

A is false but R is true.

Assertion (A): The half-life for a zero-order reaction is independent of the initial concentration of the reactant.

Reason (R): For a zero-order reaction, Rate = k

Select the most appropriate answer from the options given below:

Both A and R are true and R is the correct explanation of A.

Both A and R are true but R is not the correct explanation of A.

A is true but R is false.

A is false but R is true.

Nitrogen gas is soluble in water. At temperature 293 K, the value of K_H is 76.48 k bar. How would the solubility of nitrogen vary (increase, decrease or remain the same) at a temperature above 293 K if the value of K_H rises to 88.8 k bar?

Chloroform (b.p. 61.2°C) and acetone (b.p. 56°C) are mixed to form an azeotrope. The mole fraction of acetone in this mixture is 0.339. Predict whether the boiling point of the azeotrope formed will be

1. 60°C
2. 64.5°C or
3. 54°C

Defend your answer with reason.

A soda bottle will go flat (loose its fizz) faster in Srinagar than in Delhi. Is this statement correct? Why or why not?

How does sugar help in increasing the shelf life of the product?

Write the IUPAC name of the following complex:

\[\ce{K[Cr(H2O)2(C2O4)2]H2O}\]

Name the metal present in the complex compound of Haemoglobin.

Name the metal present in the complex compound of Vitamin B-12.

Observe the following cell and answer the questions that follow:

1. Represent the cells shown in the figure.
2. Name the carriers of the current in the salt bridge.
3. Write the reaction taking place at the anode.

Complete the following reaction by writing the major and minor products in the given case. 

\[\ce{CH3CH2Br + KCN ->}\]

Complete the following reaction by writing the major and minor products in the given case.

\[\ce{CH3CH2CH = CH2 + HBr ->}\]

Complete the following reaction by writing the major and minor products in the given case.

\[\ce{(CH3)2CHCHClCH3 + alc KOH ->}\]

The presence of carbonyl group in glucose is confirmed by its reaction with hydroxylamine. Identify the type of carbonyl group present and its position. Give a chemical reaction in support of your answer.

Write down the reaction occurring on two inert electrodes when electrolysis of copper chloride is done. What will happen if a concentrated solution of copper sulphate is replaced with copper chloride?

Write an expression for the molar conductivity of aluminium sulphate at infinite dilution according to Kohlrausch law.

Give an example and suggest a reason for the following feature of the transition metal chemistry:

The lowest oxide of transition metal is basic, the highest is amphoteric/acidic.

Account for the following:

Chromium is a hard metal, while mercury is a liquid metal.

Account for the following:

The ionisation energy of elements of the 3d series does not vary much with increasing atomic number.

Give the chemical reaction involved when p-nitrotoluene undergoes the Etard reaction.

Why does Benzoic acid exist as a dimer in an aprotic solvent?

Benzene on reaction with methylchloride in the presence of anhydrous \[\ce{AICI}\], forms toluene. What is the expected outcome if benzene is replaced by benzoic acid? Give a reason for your answer.

An organic compound ‘X’, does not undergo aldol condensation. However, ‘X’ with compound ‘Y’ in the presence of a strong base reacts to give the compound 1, 3-diphenylprop-2-en-1-one.

1. Identify 'X’ and Y’.
2. Write the chemical reaction involved. 
3. Give one chemical test to distinguish between X and Y.

Write the structure of all possible dipeptides which can be obtained from glycine and alanine.

Keratin, insulin, and myosin are a few examples of proteins present in the human body. Identify which type of protein is keratin and insulin and differentiate between them based on their physical properties.

Neeta was experimenting in the lab to study the chemical reactivity of alcohol. She carried out a dehydration reaction of propanol at 140°C to 180°C. Different products were obtained at these two temperatures.

1. Identify the major product formed at 140°C and the mechanism followed in this case.
2. Identify the major product formed at 180°C.

Various isomeric haloalkanes with the general formula \[\ce{C4H9Cl}\] undergo hydrolysis reactions. Among them, compound “A” is the most reactive through S_N1 mechanism. Identify “A” citing the reason for your choice. Write the mechanism for the reaction.

The equilibrium constant of a cell reaction:

\[\ce{Sn^{4+}(aq) + Al(s) -> Al^{3+} + Sn^{2+}(aq)}\] is 4.617 × 10¹⁸⁴, at 25°C.

1. Calculate the standard emf of the cell.
   (Given: log 4.617 × 10¹⁸⁴ = 184.6644)
2. What will be the E⁰ of the half cell \[\ce{Al^{3+}/Al}\], if the E⁰ of the half cell \[\ce{Sn^{4+}/Sn^{2+}}\] is 0.15 V.

Read the passage carefully and answer the questions that follow.

1. Predict the expression for the rate of reaction and order for the following: 
   \[\ce{H2 + Br2 -> 2HBr}\]
   What are the units of rate constant for the above reaction?  
2. How will the rate of reaction be affected if the concentration of \[\ce{Br2}\] is tripled? 
                                               OR
   What change in the concentration of \[\ce{H2}\] will triple the rate of reaction?
3. Suppose a reaction between A and B was experimentally found to be first-order with respect to both A and B. So the rate equation is:
   Rate = k[A][B]
   Which of these two mechanisms is consistent with this experimental finding? Why?
   Mechanism 1
   \[\ce{A -> C + D (slow)}\]
   \[\ce{B + C -> E (fast)}\]
   Mechanism 2
   \[\ce{A + B -> C + D (slow)}\]
   \[\ce{C -> E (fast)}\]

Amines are basic in nature. The pK_b value is a measure of the basic strength of an amine. Lower the value of pK_b, more basic is the amine. The effect of substituent on the basic strength of amines in aqueous solution was determined using titrations. The substituent “X” replaced \[\ce{^”-CH2^“}\] group in piperidine (compound 1) and propylamine \[\ce{CH3CH2CH2NH2}\], (compound 2).

Compound 1: 

Compound 2: \[\ce{HXCH2CH2NH2}\]

The experimental data is tabulated below:

Substituent “X”	Electro-negativity of X	Substituted piperidine compound	pKa	Substituted propylamine compound	pKa
\[\ce{CH2}\]	2.55		11.13	\[\ce{CH3CH2CH2NH2}\]	10.67
\[\ce{NH}\]	3.12		9.81	\[\ce{NH2CH2CH2NH2}\]	10.08
\[\ce{O}\]	3.44		8.36	\[\ce{HOCH2CH2NH2}\]	9.45
\[\ce{CH3CON}\]	3.6		7.94	\[\ce{CH3CONHCH2CH2NH2}\]	9.28
\[\ce{C6H5CON}\]	3.7		7.78	\[\ce{C6H5CONHCH2CH2NH2}\]	______

Study the above data and answer the following questions:

a. Plot a graph between the electro-negativity of the substituent vs. the pK_b value of the corresponding substituted propyl amine (given that pK_a + pK_b = 14). Is there any relation between the electro-negativity of the substituent and its basic strength?  

b. The electronegativity of the substituent \[\ce{^“C6H5CON^“}\] is 3.7; what is the expected pK_a value of compound \[\ce{C6H5CONHCH2CH2NH2}\]?

1. 9.9
2. 9.5
3. 9.3
4. 9.1

c. The pK_a value of the substituted piperidine formed with the substituent “X” is found to be 8.28. What is the expected electronegativity of “X”?

1. 3.5
2. 3.4
3. 3.8
4. 3.1

OR

What is the most suitable pK_a value of the substituted propylamine formed with substituent “X” with electronegativity 3.0?

1. 10.67
2. 10.08
3. 10.15
4. 11.10

1. Apurple colour compound A, which is a strong oxidising agent and used for bleaching of wool, cotton, silk and other textile fibres, was added to each of the three test tubes along with \[\ce{H2SO4}\]. It was followed by strong heating.
   
   In which of the above test tubes, A, B or C:
   
   1. Violet vapours will be formed.
   2. The bubbles of gas evolved will extinguish a burning matchstick. Write an equation for each of the above observations.
2. A metal ion \[\ce{M^{n+}}\] of the first transition series having d⁵ configuration combines with three didentate ligands. Assuming Δ₀ < P:
   
   1. Draw the crystal field energy level diagram for the 3d orbital of this complex.
   2. What is the hybridisation of \[\ce{M^{n+}}\] in this complex and why?
   3. Name the type of isomerism exhibited by this complex.

a. Using, Valence Bond Theory identify A, B, C, D, E and F in the following table:

b. Write the ionic equations for the reaction of acidified \[\ce{K2Cr2O7}\] with

1. \[\ce{H2S}\] and
2. \[\ce{FeSO4}\]

Give reasons for the following:

The reaction of ethanol with acetyl chloride is carried out in the presence of pyridine.

Give reasons for the following:

Cresols are less acidic than phenol.

Williamson's process is used for the preparation of ethers from alkyl halide. Identify the alkyl bromide and sodium alkoxide used for the preparation of 2-Ethoxy-3-methylpentane.

Convert Toluene to 3-nitrobenzoic acid.

Convert Benzene to m-nitroacetophenone.

Out of formic acid and acetic acid, which one will give the HVZ reaction? Give a suitable reason in support of your answer and write the chemical reaction involved.

Alcohols are acidic but they are weaker acids than water. Arrange various isomers of butanol in the increasing order of their acidic nature. Give a reason for the same.

An organic compound A which is a Grignard reagent is used to obtain 2-methylbutan-2-ol on reaction with a carbonyl compound ‘B’. Identify A’ and ‘B’. Write the equation for the reaction between A and B.

An experiment was carried out in the laboratory to study depression in freezing point. 1 M aqueous solution of \[\ce{Al(NO3)3}\] and 1 M aqueous solution of glucose were taken. From the given figure, identify solution 1 and solution 2. Give a plausible reason for your answer.

The osmotic pressure of a solution of cane sugar was found to be 2.46 atm at 300 K. If the solution was diluted five times, calculate the osmotic pressure at the same temperature.
How can the osmotic pressure of the given cane sugar solution be decreased without changing its volume? Give a reason for your answer.

While giving intravenous injections to the patients, the doctors take utmost care of the concentration of the solution used. Why is it necessary to check the concentration of the solution?

A solution of phenol was obtained by dissolving 2 × 10^-2 kg of phenol in 1 kg of benzene. Experimentally, it was found to be 73% associated. Calculate the depression in the freezing point recorded.