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Chemistry notes and chapter-wise MCQs

Read our free interactive notes, then test yourself with 24 original MCQs, chapter by chapter. Every answer is explained so that a wrong answer teaches you something.

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By Poovarasan Ramasamy, M.Sc., B.Ed. (Chemistry) · Updated October 2026

Free Chemistry notes

Our notes are written by our lecturers and open in your browser. Several include animations and practice questions placed under each topic.

Organic Chemistry

Reaction Mechanisms

Addition, elimination and substitution, built step by step with curly-arrow animations and energy profiles.

 Physical Chemistry · Class 11

Chemical Thermodynamics

First law to Gibbs energy, with 23 animations, 129 exam questions, sign charts and a formula sheet.

More chapters are being added. All notes are also listed in the Elementize Notes section of our home page.

Chapter-wise MCQs

24 questions from Class 11 and Class 12 Chemistry, written by Elementize. Try each question before opening the answer.

Some Basic Concepts of Chemistry

Class 11 · 2 questions

Q1How many moles of oxygen atoms are present in 0.5 mol of CO2?

  1. 0.25
  2. 0.5
  3. 1
  4. 2
Show answer

Answer: (C) Each CO2 molecule has 2 O atoms, so 0.5 mol CO2 contains 2 × 0.5 = 1 mol of O atoms.

Q2What is the mass of 3.011 × 1023 molecules of water?

  1. 4.5 g
  2. 9 g
  3. 18 g
  4. 36 g
Show answer

Answer: (B) 3.011 × 1023 is half of Avogadro's number, so this is 0.5 mol. Mass = 0.5 × 18 g mol−1 = 9 g.

Structure of Atom

Class 11 · 2 questions

Q3What is the maximum number of electrons in the shell with n = 3?

  1. 8
  2. 9
  3. 18
  4. 32
Show answer

Answer: (C) A shell can hold 2n2 electrons: 2 × 32 = 18.

Q4Which set of quantum numbers is NOT possible?

  1. n = 2, l = 1, m = 0
  2. n = 3, l = 2, m = −2
  3. n = 2, l = 2, m = 1
  4. n = 4, l = 0, m = 0
Show answer

Answer: (C) l can take values from 0 to n − 1. For n = 2, l can only be 0 or 1, so l = 2 is not allowed.

Chemical Bonding and Molecular Structure

Class 11 · 2 questions

Q5What is the shape of XeF4?

  1. Tetrahedral
  2. Square planar
  3. See-saw
  4. Octahedral
Show answer

Answer: (B) Xe has 4 bond pairs and 2 lone pairs (6 electron pairs, sp3d2). The lone pairs sit opposite each other, giving a square planar shape.

Q6What is the bond order of O2+?

  1. 1.5
  2. 2
  3. 2.5
  4. 3
Show answer

Answer: (C) O2 has bond order 2. Removing one electron from an antibonding π* orbital raises it to (10 − 5) / 2 = 2.5.

Thermodynamics

Class 11 · 2 questions

Q7At constant temperature and pressure, a process is spontaneous when:

  1. ΔG > 0
  2. ΔG = 0
  3. ΔG < 0
  4. ΔH > 0
Show answer

Answer: (C) At constant T and P, a decrease in Gibbs energy (ΔG < 0) is the condition for a spontaneous process. ΔG = 0 means equilibrium.

Q8For N2(g) + 3H2(g) → 2NH3(g), how are ΔH and ΔU related?

  1. ΔH = ΔU
  2. ΔH = ΔU + 2RT
  3. ΔH = ΔU − 2RT
  4. ΔH = ΔU − RT
Show answer

Answer: (C) ΔH = ΔU + ΔngRT. Here Δng = 2 − 4 = −2, so ΔH = ΔU − 2RT.

Equilibrium

Class 11 · 2 questions

Q9What is the pH of 0.001 M HCl at 25 °C?

  1. 1
  2. 2
  3. 3
  4. 11
Show answer

Answer: (C) HCl is a strong acid, so [H+] = 10−3 M and pH = −log(10−3) = 3.

Q10An inert gas is added at constant volume to N2 + 3H2 ⇌ 2NH3 at equilibrium. The equilibrium:

  1. Shifts forward
  2. Shifts backward
  3. Does not change
  4. Shifts forward only at high temperature
Show answer

Answer: (C) At constant volume the partial pressures (concentrations) of the reacting gases do not change, so the equilibrium is undisturbed.

Electrochemistry

Class 12 · 2 questions

Q11How many faradays are needed to deposit 1 mol of aluminium from Al3+ ions?

  1. 1 F
  2. 2 F
  3. 3 F
  4. 6 F
Show answer

Answer: (C) Al3+ + 3e− → Al, so 3 mol of electrons, or 3 F, deposit 1 mol of Al.

Q12When a solution of a weak electrolyte is diluted, which of these increases?

  1. Conductivity (κ)
  2. Molar conductivity (Λm)
  3. Number of ions per unit volume
  4. Concentration
Show answer

Answer: (B) Dilution increases the degree of dissociation, so molar conductivity rises. Conductivity falls because there are fewer ions per unit volume.

Chemical Kinetics

Class 12 · 2 questions

Q13A first-order reaction has a half-life of 10 min. How long does 75% completion take?

  1. 15 min
  2. 20 min
  3. 30 min
  4. 40 min
Show answer

Answer: (B) 75% completion means 25% remains, which is two half-lives: 2 × 10 min = 20 min.

Q14What are the units of the rate constant for a zero-order reaction?

  1. s−1
  2. mol L−1 s−1
  3. L mol−1 s−1
  4. L2 mol−2 s−1
Show answer

Answer: (B) For a zero-order reaction, rate = k, so k has the units of rate: mol L−1 s−1.

Coordination Compounds

Class 12 · 2 questions

Q15What is the oxidation state of iron in K4[Fe(CN)6]?

  1. +2
  2. +3
  3. +4
  4. +6
Show answer

Answer: (A) 4(+1) + x + 6(−1) = 0, so x = +2.

Q16[Co(NH3)6]3+ is:

  1. Paramagnetic, outer-orbital (sp3d2)
  2. Diamagnetic, inner-orbital (d2sp3)
  3. Paramagnetic, inner-orbital
  4. Diamagnetic, outer-orbital
Show answer

Answer: (B) Co3+ is d6. NH3 pairs up the electrons, leaving two empty 3d orbitals for d2sp3 hybridisation. With no unpaired electrons, the complex is diamagnetic.

Organic Chemistry: Basic Principles (GOC)

Class 11 · 2 questions

Q17Which carbocation is the most stable?

  1. CH3+
  2. CH3CH2+
  3. (CH3)2CH+
  4. (CH3)3C+
Show answer

Answer: (D) The tertiary carbocation has the most hyperconjugation and +I effect from three methyl groups, so it is the most stable.

Q18Which group shows both a −I effect and a +R (resonance) effect?

  1. –NO2
  2. –CHO
  3. –Cl
  4. –CH3
Show answer

Answer: (C) Chlorine is electronegative (−I) but donates a lone pair into a π system (+R). –NO2 and –CHO are −I and −R; –CH3 is +I.

Haloalkanes and Haloarenes

Class 12 · 2 questions

Q19(R)-2-Bromobutane reacts with aqueous OH− by an SN2 mechanism. The product is:

  1. (R)-Butan-2-ol
  2. (S)-Butan-2-ol
  3. A racemic mixture
  4. But-2-ene
Show answer

Answer: (B) SN2 goes with backside attack and inversion of configuration, so the R reactant gives (S)-butan-2-ol.

Q20Which compound reacts fastest by the SN1 mechanism?

  1. CH3Br
  2. CH3CH2Br
  3. (CH3)2CHBr
  4. (CH3)3CBr
Show answer

Answer: (D) SN1 goes through a carbocation, and the tertiary carbocation from (CH3)3CBr is the most stable.

Aldehydes, Ketones and Carboxylic Acids

Class 12 · 2 questions

Q21Which compound gives a positive iodoform test?

  1. Methanol
  2. Ethanol
  3. Propan-1-ol
  4. Benzaldehyde
Show answer

Answer: (B) Ethanol is oxidised to CH3CHO, which has the CH3CO– group needed for the iodoform reaction. The others cannot form it.

Q22Which compound undergoes the Cannizzaro reaction?

  1. CH3CHO
  2. HCHO
  3. CH3COCH3
  4. CH3CH2CHO
Show answer

Answer: (B) The Cannizzaro reaction needs an aldehyde with no α-hydrogen. HCHO has none; the others can undergo aldol condensation instead.

Amines

Class 12 · 1 question

Q23Which is the strongest base in aqueous solution?

  1. NH3
  2. CH3NH2
  3. (CH3)2NH
  4. (CH3)3N
Show answer

Answer: (C) In water, the combined effect of +I, solvation of the ammonium ion and steric hindrance makes the secondary amine the strongest: (CH3)2NH > CH3NH2 > (CH3)3N > NH3.

Biomolecules

Class 12 · 1 question

Q24On prolonged heating with HI, glucose gives:

  1. n-Hexane
  2. Gluconic acid
  3. Saccharic acid
  4. Sorbitol
Show answer

Answer: (A) Prolonged heating with HI reduces glucose to n-hexane, showing that its six carbon atoms are joined in a straight chain.

How to use these questions

  • Answer first, then check. Opening the answer too early turns practice into reading.
  • Read the explanation even when you are right. You may have chosen the right option for the wrong reason.
  • Keep an error log. Note the chapter and why you went wrong: concept, calculation or misreading.
  • Go back to the chapter. If you miss both questions from a chapter, revise it before moving on.

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