Author: Sarvan Kumar

Sarvan Kumar http://sarvankumar.wordpress.com My name is Sarvan Kumar, I am post graduate in chemistry (MSc). besides teaching chemistry at various schools and coaching centres I have been giving home tuitions to students for 10 years. I have helped students score good marks in chemistry not only in board examination but also JEE, NEET, SAT, IGCSE and IB examinations. Nearly 90% of my students have scored more than 95% in their CBSE board examination. Moreover they have also secured a seat in prestigious engineering and medical college. Since every student is different hence my unique style of teach

MCQs – Alcohols, Phenols & Ethers

1. Which of the following will show hydrogen bonding?
a) CH₃–O–CH₃
b) CH₃–CH₂–OH
c) C₆H₆
d) CH₃Cl

2. The decreasing order of acidic strength is:
a) Water > Phenol > Alcohol
b) Phenol > Alcohol > Water
c) Phenol > Water > Alcohol
d) Alcohol > Phenol > Water

3. Which alcohol gives a yellow precipitate with iodine and NaOH (iodoform test)?
a) Ethanol
b) Methanol
c) n–propanol
d) Benzyl alcohol

4. Which one gives a violet colour with neutral FeCl₃ solution?
a) Ethanol
b) Phenol
c) Methanol
d) Diethyl ether

5. In Williamson synthesis, ethers are prepared by the reaction of:
a) Alcohol with halogen
b) Alcohol with alkyl halide in presence of base
c) Phenol with alkyl halide in presence of base
d) Both (b) and (c)

6. Phenol reacts with NaOH to form:
a) C₆H₅ONa
b) C₆H₆
c) C₆H₅Cl
d) C₆H₅NO₂

7. Phenol on reaction with conc. HNO₃ gives:
a) o–Nitrophenol
b) p–Nitrophenol
c) 2,4,6–Trinitrophenol
d) m–Nitrophenol

8. Which compound is used in the manufacture of Bakelite?
a) Phenol + Formaldehyde
b) Phenol + Acetaldehyde
c) Ethanol + Formaldehyde
d) Phenol + Methanol

9. Which is more acidic?
a) Ethanol
b) Phenol
c) Water
d) Methanol

10. Which of the following alcohols is tertiary?
a) CH₃CH₂CH₂OH
b) (CH₃)₂CH–OH
c) (CH₃)₃C–OH
d) CH₃OH

11. Phenol undergoes electrophilic substitution easily because:
a) –OH group decreases electron density
b) –OH group activates the ring towards electrophilic substitution
c) –OH group withdraws electrons
d) None of these

12. Phenol + Br₂ water gives:
a) p–Bromophenol
b) o–Bromophenol
c) 2,4,6–Tribromophenol
d) Bromobenzene

13. Lucas test is used to distinguish between:
a) Primary, secondary and tertiary alcohols
b) Alcohols and phenols
c) Alcohols and ethers
d) Primary and secondary alcohols only

14. The product formed when anisole (C₆H₅–OCH₃) reacts with HI is:
a) C₆H₅I + CH₃OH
b) C₆H₅OH + CH₃I
c) C₆H₆ + HI
d) C₆H₅I + CH₄

15. The IUPAC name of glycerol is:
a) Propan-1,2,3-triol
b) Propanol
c) Butan-1,2,3-triol
d) Ethane-1,2-diol

16. Which reagent is used to convert alcohols into aldehydes and ketones?
a) PCC (Pyridinium chlorochromate)
b) Zn/HCl
c) NaBH₄
d) LiAlH₄

17. When ethanol is treated with hot concentrated H₂SO₄, the major product is:
a) Ethene
b) Ethane
c) Ether
d) Acetaldehyde

18. Which one of the following is NOT an isomer of C₄H₁₀O?
a) Diethyl ether
b) Butan-1-ol
c) Butan-2-ol
d) Propan-2-ol

19. Phenol reacts with Zn dust to form:
a) Benzene
b) Toluene
c) Benzyl alcohol
d) Benzoic acid

20. Which of the following will have highest boiling point?
a) CH₃OH
b) CH₃–O–CH₃
c) C₂H₆
d) CH₃Cl

✅ Answer Key

  1. b
  2. c
  3. a
  4. b
  5. d
  6. a
  7. c
  8. a
  9. b
  10. c
  11. b
  12. c
  13. a
  14. b
  15. a
  16. a
  17. a
  18. d
  19. a
  20. a

MCQs – Haloalkanes & Haloarenes Class 12

MCQs – Haloalkanes & Haloarenes

1. The general formula of alkyl halide is:
a) CnH₂n+₂X
b) CnH₂n+1X
c) CnH₂n–1X
d) CnH₂nX

2. Which of the following alkyl halides undergoes SN1 reaction most readily?
a) CH₃Cl
b) CH₃CH₂Cl
c) (CH₃)₃CCl
d) CH₃CH₂CH₂Cl

3. Which of the following is most reactive towards nucleophilic substitution?
a) Benzyl chloride
b) Vinyl chloride
c) Aryl chloride
d) Chlorobenzene

4. Which of the following haloalkanes is most reactive towards β–elimination?
a) 1-chlorobutane
b) 2-chlorobutane
c) 2-chloro-2-methylpropane
d) Chloromethane

5. The C–X bond strength in haloalkanes decreases in the order:
a) C–I > C–Br > C–Cl > C–F
b) C–F > C–Cl > C–Br > C–I
c) C–Cl > C–F > C–Br > C–I
d) C–Br > C–Cl > C–F > C–I

6. The Wurtz reaction is used to prepare:
a) Alkanes
b) Alkenes
c) Alcohols
d) Ethers

7. Chlorobenzene is less reactive towards nucleophilic substitution due to:
a) Resonance
b) High bond dissociation energy of C–Cl
c) Partial double bond character of C–Cl bond
d) All of these

8. Which of the following is used as a refrigerant (Freon)?
a) CCl₄
b) CF₂Cl₂
c) CHCl₃
d) CH₂Cl₂

9. Which of the following is called “methylating agent”?
a) CH₃I
b) CH₃Cl
c) CH₃Br
d) CH₃F

10. Iodoform test is given by:
a) CH₃CH₂Cl
b) CH₃Cl
c) CH₃CH(OH)CH₃
d) CH₃CH₂I

11. Chloroform on oxidation with air and light gives a poisonous gas:
a) COCl₂
b) HCl
c) Cl₂
d) CHCl₃O

12. Which of the following is used as an anaesthetic?
a) CCl₄
b) CHCl₃
c) CF₂Cl₂
d) C₂H₅Cl

13. Which one is used as a solvent in dry cleaning?
a) CHCl₃
b) CCl₄
c) C₂H₅Cl
d) CH₂Cl₂

14. Which of the following shows +I effect most strongly?
a) –Cl
b) –Br
c) –I
d) –F

15. When chlorobenzene is treated with NaOH at 623 K and 300 atm, the product is:
a) Benzyl alcohol
b) Phenol
c) Benzaldehyde
d) Aniline

16. Which of the following will form Grignard reagent?
a) C₆H₆
b) CH₄
c) C₂H₅Cl
d) C₂H₅OH

17. Allyl chloride is more reactive than n-propyl chloride in nucleophilic substitution because:
a) Inductive effect
b) Hyperconjugation
c) Resonance stabilization of carbocation
d) None of these

18. Freons cause:
a) Acid rain
b) Ozone layer depletion
c) Greenhouse effect
d) Photochemical smog

19. Aryl halides are less reactive towards nucleophilic substitution than alkyl halides due to:
a) Resonance effect
b) Partial double bond character
c) Steric hindrance
d) All of the above

20. The reaction of chlorobenzene with Cl₂/FeCl₃ gives:
a) Benzyl chloride
b) Dichlorobenzene
c) Benzyl alcohol
d) Chlorotoluene

✅ Answer Key

  1. b
  2. c
  3. a
  4. c
  5. b
  6. a
  7. d
  8. b
  9. a
  10. c
  11. a
  12. b
  13. b
  14. b
  15. b
  16. c
  17. c
  18. b
  19. d
  20. b

MCQs – d-Block Elements Chemistry 12

MCQs – d & f Block Elements SET 1

1. The general electronic configuration of d-block elements is:
a) (n−1)d¹–¹⁰ ns¹–²
b) ns² np⁶
c) ns² np⁵
d) (n−2)f¹–¹⁴ (n−1)d¹–¹⁰ ns²

2. Which of the following elements shows maximum number of oxidation states?
a) Fe
b) Mn
c) Cr
d) V

3. The transition metal that does not exhibit variable oxidation states is:
a) Sc
b) Cu
c) Mn
d) Fe

4. Which ion is colourless?
a) Ti³⁺
b) V²⁺
c) Cu⁺
d) Cr³⁺

5. The catalytic properties of transition metals are due to:
a) Variable oxidation states
b) High ionisation enthalpy
c) Low electronegativity
d) Inert pair effect

6. Which of the following is a transition element?
a) Zn
b) Cd
c) Hg
d) Cu

7. The lanthanoid contraction is due to:
a) Poor shielding of 4f electrons
b) High nuclear charge
c) Relativistic effects
d) d-orbital contraction

8. The transition element used in stainless steel is:
a) Cr
b) Mn
c) Ni
d) Fe

9. Which transition metal ion is most stable due to half-filled configuration?
a) Cr³⁺
b) Fe²⁺
c) Mn²⁺
d) Ni²⁺

10. Which property is common to most transition metals?
a) They are colourless
b) They form coloured compounds
c) They are highly electropositive like alkali metals
d) They do not form complexes

11. Potassium dichromate is a strong:
a) Reducing agent in acidic medium
b) Oxidising agent in acidic medium
c) Oxidising agent in basic medium
d) Neutral compound

Answer Key

  1. a
  2. b
  3. a
  4. c
  5. a
  6. d
  7. a
  8. a
  9. c
  10. b
  11. b
  12. b
  13. c
  14. d
  15. b
  16. b
  17. a
  18. b
  19. c
  20. d

MCQs Chemical Kinetics class 12

MCQs – Chemical Kinetics

1. The unit of rate constant for a first-order reaction is:
a) mol L⁻¹ s⁻¹
b) s⁻¹
c) L mol⁻¹ s⁻¹
d) mol² L⁻² s⁻¹

2. For a zero-order reaction, the rate depends on:
a) Concentration of reactants
b) Temperature only
c) Rate constant only
d) Both concentration and rate constant

3. If half-life of a first-order reaction is 20 minutes, the rate constant is:
a) 0.0347 min⁻¹
b) 0.693 min⁻¹
c) 0.020 min⁻¹
d) 0.050 min⁻¹

4. In the Arrhenius equation k=Ae−Ea/RTk = A e^{-Ea/RT}k=Ae−Ea/RT, the slope of ln⁡k\ln klnk vs 1T\frac{1}{T}T1​ is:
a) −Ea/R-Ea/R−Ea/R
b) Ea/REa/REa/R
c) R/EaR/EaR/Ea
d) −R/Ea-R/Ea−R/Ea

5. For a reaction A→BA \to BA→B, the rate of disappearance of A is 0.03 mol L⁻¹ s⁻¹. The rate of appearance of B is:
a) 0.03 mol L⁻¹ s⁻¹
b) 0.015 mol L⁻¹ s⁻¹
c) 0.06 mol L⁻¹ s⁻¹
d) Zero

6. Which order of reaction has half-life independent of initial concentration?
a) Zero order
b) First order
c) Second order
d) Third order

7. A reaction is first order in A and zero order in B. The rate law is:
a) Rate = k[A][B]
b) Rate = k[A]
c) Rate = k[B]
d) Rate = k[A][B]⁰

8. A plot of [A][A][A] vs time is linear for:
a) Zero order reaction
b) First order reaction
c) Second order reaction
d) Third order reaction

9. The activation energy of a reaction is 50 kJ mol⁻¹. If temperature increases, rate constant will:
a) Increase
b) Decrease
c) Remain constant
d) Become zero

10. The rate constant of a reaction doubles when temperature is increased by 10°C. This is known as:
a) Van’t Hoff’s rule
b) Arrhenius rule
c) Rate law
d) Lindemann rule

11. The half-life of a zero-order reaction is given by:
a) t1/2=0.693kt_{1/2} = \dfrac{0.693}{k}t1/2​=k0.693​
b) t1/2=[A]02kt_{1/2} = \dfrac{[A]_0}{2k}t1/2​=2k[A]0​​
c) t1/2=1k[A]0t_{1/2} = \dfrac{1}{k[A]_0}t1/2​=k[A]0​1​
d) t1/2=k[A]0t_{1/2} = k[A]_0t1/2​=k[A]0​

12. The order of a reaction can be determined by:
a) Molecularity
b) Balanced chemical equation
c) Experimental data only
d) Thermodynamics

13. In a chemical reaction, doubling the concentration of reactant doubles the rate. The order is:
a) Zero
b) One
c) Two
d) Three

14. The rate constant of a first-order reaction is 0.231 min⁻¹. The half-life is:
a) 3 min
b) 10 min
c) 30 min
d) 300 min

15. Molecularity of a reaction can be:
a) Zero
b) Fractional
c) Whole number only
d) Infinite

16. For a first-order reaction, the graph between ln⁡[A]\ln [A]ln[A] and time is:
a) Straight line, positive slope
b) Straight line, negative slope
c) Curve increasing
d) Curve decreasing

17. In a reaction, rate = k[A]²[B], the overall order is:
a) 1
b) 2
c) 3
d) 0

18. Temperature dependence of rate constant is expressed by:
a) Rate law
b) Arrhenius equation
c) Collision theory
d) Gibbs free energy

19. If the rate of reaction does not change with concentration, the order is:
a) Zero
b) First
c) Second
d) Infinite

20. In pseudo-first order reactions:
a) Both reactants are first order
b) Both are zero order
c) One reactant is in large excess
d) Reaction is always second order

✅ Answer Key

  1. b
  2. c
  3. a
  4. a
  5. a
  6. b
  7. b (or d, since [B]⁰ = 1)
  8. a
  9. a
  10. a
  11. b
  12. c
  13. b
  14. b
  15. c
  16. b
  17. c
  18. b
  19. a
  20. c

MCQs on Electrochemistry – Class 12

1.

The standard electrode potential of Zn²⁺/Zn is –0.76 V and of Cu²⁺/Cu is +0.34 V. The EMF of the cell Zn | Zn²⁺ || Cu²⁺ | Cu is:
a) 1.10 V
b) –1.10 V
c) 0.42 V
d) –0.42 V

2.

Which of the following is used as a primary cell?
a) Lead storage battery
b) Nickel–cadmium cell
c) Dry cell
d) Fuel cell

3.

Kohlrausch’s law is related to:
a) Solubility product
b) Conductivity of electrolytes at infinite dilution
c) Cell potential
d) Gibbs free energy

4.

Which electrode is used in a hydrogen electrode?
a) Platinum black
b) Copper
c) Silver
d) Graphite

5.

In the Daniel cell, electrons flow from:
a) Copper to zinc
b) Zinc to copper
c) Electrolyte to copper
d) Electrolyte to zinc

6.

The relationship between ΔG° and E°cell is:
a) ΔG° = –nFE°cell
b) ΔG° = nFE°cell
c) ΔG° = –E°cell/F
d) ΔG° = –RT ln E°cell

7.

The conductivity of a solution decreases with:
a) Increase in temperature
b) Decrease in temperature
c) Increase in concentration
d) Increase in dilution

8.

At infinite dilution, molar conductivity of weak electrolyte:
a) Becomes zero
b) Becomes infinite
c) Remains constant
d) Cannot be determined directly

9.

The unit of molar conductivity (Λm) in SI is:
a) ohm⁻¹ cm⁻¹
b) ohm⁻¹ cm² mol⁻¹
c) S m² mol⁻¹
d) S cm mol⁻¹

10.

Electrochemical equivalent is expressed in:
a) g C⁻¹
b) C mol⁻¹
c) g mol⁻¹
d) g A⁻¹

11.

Which of the following cells is a fuel cell?
a) Daniel cell
b) H₂–O₂ cell
c) Dry cell
d) Lead storage battery

12.

For the reaction:
2Ag++Cu→2Ag+Cu2+2Ag^+ + Cu \rightarrow 2Ag + Cu^{2+}2Ag++Cu→2Ag+Cu2+
If E°(Ag⁺/Ag) = +0.80 V and E°(Cu²⁺/Cu) = +0.34 V, E°cell = ?
a) 0.46 V
b) 0.80 V
c) 1.14 V
d) 0.34 V

13.

Which of the following is not a secondary cell?
a) Lead–acid battery
b) Nickel–cadmium cell
c) Mercury cell
d) None of these

14.

Which of the following quantities remains constant during electrolysis?
a) Number of electrons
b) Charge of electrons
c) Mass of substance deposited
d) Volume of electrolyte

15.

Faraday’s first law of electrolysis states:
a) Mass deposited ∝ time
b) Mass deposited ∝ charge passed
c) Mass deposited ∝ atomic mass
d) Mass deposited ∝ current density

16.

In a concentration cell, EMF is:
a) Zero
b) Positive
c) Negative
d) Depends on concentration difference

17.

In the electrolysis of molten NaCl:
a) Na is liberated at cathode
b) Cl₂ is liberated at cathode
c) H₂ is liberated at anode
d) O₂ is liberated at cathode

18.

The slope of molar conductivity (Λm) vs √c graph for weak electrolytes gives:
a) Λm°
b) Limiting molar conductivity
c) Degree of dissociation
d) Ionic conductivity

19.

The resistance of a conductivity cell filled with 0.1 M KCl solution is 100 Ω. The cell constant is 1.29 cm⁻¹. What is the conductivity (κ)?
a) 0.0129 S cm⁻¹
b) 0.129 S cm⁻¹
c) 0.00129 S cm⁻¹
d) 1.29 S cm⁻¹

20.

In a galvanic cell, salt bridge is used to:
a) Maintain electrical neutrality
b) Increase EMF
c) Provide electrons
d) Prevent leakage of solution

21.

Which of the following has the highest molar conductivity at infinite dilution?
a) NaCl
b) KCl
c) LiCl
d) CsCl

22.

The quantity of electricity required to deposit 1 mole of silver (Ag⁺ + e⁻ → Ag) is:
a) 96500 C
b) 48250 C
c) 193000 C
d) 965 C

23.

The decrease in molar conductivity of a strong electrolyte with increase in concentration is due to:
a) Decrease in number of ions
b) Increase in ionic mobility
c) Increase in inter-ionic attraction
d) Increase in solvation

24.

The emf of a galvanic cell is related to equilibrium constant (K) by:
a) E°cell = RT/nF ln K
b) E°cell = –RT/nF ln K
c) nFE°cell = RT ln K
d) ΔG° = –RT ln K

25.

Which of the following metals is extracted by electrolysis of its molten salt?
a) Copper
b) Silver
c) Sodium
d) Iron

Answer Key

  1. a
  2. c
  3. b
  4. a
  5. b
  6. a
  7. c
  8. d
  9. c
  10. a
  11. b
  12. a
  13. c
  14. b
  15. b
  16. d
  17. a
  18. c
  19. a
  20. a
  21. d
  22. a
  23. c
  24. c
  25. c

MCQs on Solutions – Class 12

MCQs on Solutions – Class 12

1.

If 2 moles of NaCl are dissolved in 1 kg of water, the molality of the solution is:
a) 1 m
b) 2 m
c) 0.5 m
d) 4 m

2.

Which of the following is not a colligative property?
a) Relative lowering of vapour pressure
b) Osmotic pressure
c) Depression of freezing point
d) Molal mass

3.

A 0.1 M solution of glucose and a 0.1 M solution of NaCl are prepared. Which will have higher osmotic pressure?
a) Glucose
b) NaCl
c) Both same
d) Cannot be predicted

4.

The vapour pressure of pure water at 25 °C is 23.8 mmHg. What will be the vapour pressure of a solution containing 1 mol of non-volatile solute in 55.5 mol of water?
a) 23.38 mmHg
b) 23.0 mmHg
c) 22.0 mmHg
d) 21.5 mmHg

5.

Henry’s law constant for CO₂ in water is high. This means:
a) CO₂ is very soluble in water
b) CO₂ is sparingly soluble in water
c) Solubility is independent of pressure
d) Solubility increases rapidly with temperature

6.

If 1 mole of NaCl is dissolved in 1 L water, the van’t Hoff factor (i) is:
a) 1
b) 2
c) 3
d) 0

7.

A solution boils at 100.52 °C. The ebullioscopic constant of water (Kb) = 0.52 K kg mol⁻¹. The molality of solute is:
a) 1 m
b) 0.5 m
c) 2 m
d) 0.1 m

8.

Which statement is correct?
a) Colligative properties depend on nature of solute.
b) Colligative properties depend on number of solute particles.
c) Colligative properties depend on solvent only.
d) Colligative properties are independent of concentration.

9.

The mole fraction of solute in a solution is 0.2. What is the mole fraction of solvent?
a) 0.8
b) 0.2
c) 1.2
d) 0.02

10.

A 5% (w/w) solution of glucose in water means:
a) 5 g glucose in 95 g water
b) 5 g glucose in 100 g solution
c) 5 g glucose in 100 mL solution
d) 5 g glucose in 100 g water

11.

The units of Henry’s law constant KH are:
a) mol L⁻¹ atm⁻¹
b) atm mol⁻¹ L
c) atm
d) mol L⁻¹

12.

An azeotrope is:
a) A mixture of liquids with the same composition in liquid and vapour phase
b) A mixture that boils at variable temperature
c) A mixture of solid and liquid
d) A mixture showing abnormal colligative properties

13.

Which of the following pairs shows positive deviation from Raoult’s law?
a) H₂O + C₂H₅OH
b) CHCl₃ + C₆H₆
c) H₂O + HCl
d) Acetone + CS₂

14.

Relative lowering of vapour pressure is equal to:
a) Mole fraction of solute
b) Mole fraction of solvent
c) Molality of solution
d) Molarity of solution

15.

The freezing point of 1 molal NaCl solution is nearly double the depression shown by 1 molal urea solution. Why?
a) NaCl is volatile
b) NaCl ionises giving more particles
c) NaCl reduces vapour pressure more
d) NaCl is heavier

16.

At higher altitudes, people use pressure cookers because:
a) Boiling point of water increases with pressure
b) Boiling point of water decreases with pressure
c) Vapour pressure of water decreases with temperature
d) None of the above

17.

The value of van’t Hoff factor (i) for K₂SO₄ is:
a) 2
b) 3
c) 1
d) 4

18.

Which one forms a maximum boiling azeotrope with water?
a) HNO₃
b) HCl
c) C₂H₅OH
d) CH₃COOH

19.

The molarity of pure water is approximately:
a) 1 M
b) 18 M
c) 55.5 M
d) 100 M

20.

If osmotic pressure of 0.01 M solution of a substance is 2.46 atm at 27 °C, the substance is:
(R = 0.0821 L atm K⁻¹ mol⁻¹)
a) Nonelectrolyte
b) Strong electrolyte
c) Non-volatile liquid
d) Colloid

21.

Cryoscopic constant (Kf) depends on:
a) Nature of solute
b) Nature of solvent
c) Both solute and solvent
d) Temperature only

22.

If solute associates in a solution, van’t Hoff factor (i) is:
a) > 1
b) < 1
c) = 1
d) Infinite

23.

In osmosis, solvent moves:
a) From concentrated solution to dilute
b) From dilute solution to concentrated
c) From high pressure to low pressure
d) In both directions equally

24.

Raoult’s law is applicable to:
a) Non-ideal solutions only
b) Ideal solutions only
c) Electrolyte solutions
d) Colloidal solutions

25.

A solution shows negative deviation from Raoult’s law when:
a) A–B interactions < A–A or B–B
b) A–B interactions > A–A or B–B
c) Solution behaves ideally
d) Solute associates in solution

Answer Key

  1. b
  2. d
  3. b
  4. a
  5. b
  6. b
  7. a
  8. b
  9. a
  10. b
  11. a
  12. a
  13. d
  14. a
  15. b
  16. a
  17. b
  18. a
  19. c
  20. b
  21. b
  22. b
  23. b
  24. b
  25. b

what is carbene? Singlet carbene and Triplet carbene

A carbene is a highly reactive organic species in which a carbon atom has only six valence electrons (instead of the usual eight) and is bonded to two substituents.

General Features:

  • General formula: R₂C:
  • Structure: Carbon in carbene is divalent (forms 2 bonds).
  • Electron deficiency: Only 6 valence electrons → makes carbenes very reactive.
  • Bond angle: Usually about 104–150°, depending on type.

Types of Carbenes:

  1. Singlet carbene
    • Both non-bonded electrons are paired in the same orbital.
    • Usually bent structure (~104° bond angle).
    • Electrophilic (electron-loving).
  2. Triplet carbene
    • The two non-bonded electrons occupy different orbitals with parallel spins.
    • Linear or nearly linear structure (~130–150° bond angle).
    • More stable than singlet.

Examples:

  • Methylene (:CH₂) → simplest carbene.
  • Dichlorocarbene (:CCl₂) → formed in Reimer–Tiemann reaction.

Preparation:

  • By photolysis or pyrolysis of diazo compounds (e.g., CH₂N₂ → :CH₂ + N₂).
  • By decomposition of haloforms (CHCl₃ + base → :CCl₂).

Reactivity:

  • Carbenes add to double bonds → form cyclopropanes.
  • Insert into C–H bonds.
  • Highly reactive intermediates in organic chemistr

Aakash NEET Question Paper 2025 With solution pdf

Aakash NEET‑UG 2025 Question Paper & Solutions – Code 45

The Aakash Institute has officially released the detailed question papers and solutions for the NEET‑UG 2025 examination held on May 4, 2025, in sets 45. This comprehensive PDFs include full-colour answer keys and step-by-step explanations, carefully prepared by subject-matter experts to help aspirants evaluate their performance and fine-tune their NEET preparation strategies

What’s inside the downloads?

  • Code-specific coverage: Available for Booklet Code 45 ensuring accuracy for your specific question set .
  • Physics, Chemistry & Biology: PDF contains all 180 MCQs along with fully worked-out solutions—including diagrams, formulas, and calculations.
NEET Question Paper 2025Download

Define catalyst give two examples

A catalyst is a substance that increases the rate of a chemical reaction by providing an alternative reaction pathway with a lower activation energy, without being consumed in the process. Catalysts work by facilitating the formation of the transition state, enabling the reaction to proceed more rapidly. They remain unchanged chemically and are not consumed during the reaction, allowing them to participate in multiple reaction cycles.

Two examples of catalysts are:

  1. Enzymes: Enzymes are biological catalysts that facilitate and regulate biochemical reactions in living organisms. They are typically proteins that act as catalysts by lowering the activation energy required for specific reactions. Enzymes play a crucial role in various biological processes such as digestion, metabolism, and DNA replication. For example, the enzyme amylase catalyzes the hydrolysis of starch into smaller sugar molecules.
  2. Platinum in Catalytic Converters: Platinum and other precious metals (such as palladium and rhodium) are commonly used as catalysts in catalytic converters of automobiles. They facilitate the conversion of harmful pollutants from exhaust gases into less harmful substances. For instance, platinum catalysts help to convert carbon monoxide (CO) into carbon dioxide (CO2) and nitrogen oxides (NOx) into nitrogen (N2) and oxygen (O2), reducing their environmental impact.

These examples demonstrate how catalysts can significantly enhance reaction rates and enable chemical transformations without being consumed in the process, making them crucial in various industrial, environmental, and biological applications.

Difference between adsorption and absorption

Adsorption and absorption are two distinct processes that involve the interaction of substances with a solid or liquid surface. Here are the key differences between adsorption and absorption:

  1. Nature of Interaction:
  • Adsorption: Adsorption refers to the adherence or accumulation of atoms, ions, or molecules from a gas or liquid phase onto the surface of a solid or liquid. It involves weak intermolecular forces of attraction between the adsorbate and the adsorbent. The adsorbate remains on the surface without penetrating or entering the interior of the adsorbent material.
  • Absorption: Absorption involves the penetration or uptake of a substance (liquid or gas) into the bulk of a solid or liquid material. The absorbed substance disperses within the absorbing material, entering its interior or matrix. Absorption can involve dissolution of the absorbed substance in the absorbing material.
  1. Surface Area:
  • Adsorption: Adsorption occurs specifically at the surface of the adsorbent material, taking place only on the exposed surface area. The concentration of the adsorbate is generally higher at the surface compared to the bulk.
  • Absorption: Absorption occurs throughout the bulk of the absorbing material, not limited to the surface area. The absorbed substance permeates or disperses within the absorbing material.
  1. Reversibility:
  • Adsorption: Adsorption is typically a reversible process, meaning that the adsorbate can be desorbed or removed from the surface under suitable conditions, such as changes in temperature or pressure.
  • Absorption: Absorption is not necessarily a reversible process. The absorbed substance may remain within the bulk of the absorbing material and might not be easily released.
  1. Energy Involved:
  • Adsorption: Adsorption generally involves weak intermolecular forces (such as van der Waals forces) between the adsorbate and the adsorbent. The energy associated with adsorption is lower than that of chemical bonds.
  • Absorption: Absorption often involves stronger interactions, such as chemical bonds or intermolecular forces, between the absorbed substance and the absorbing material. The energy associated with absorption is generally higher than that of adsorption.

In summary, adsorption refers to the adherence of substances onto a surface, occurring at the surface and involving weak intermolecular forces. Absorption, on the other hand, involves the penetration of substances into the bulk of a material, occurring throughout the material and often involving stronger interactions.