🧪 "Crack the Code: Step-by-Step Solutions to NSSCAS Chemistry Past Paper 1 Exam Questions 2024 (With Expert Answers)"

  

Certainly! Let's go through each question step by step, explaining how to derive the correct answers.

Question 1

Question: Acetophenone, C₆H₈O, is an organic compound. What is the percentage by mass of hydrogen in acetophenone?

Options:
A. 6.7 %
B. 8.0 %
C. 10 %
D. 22 %

Answer: A. 6.7 %

Explanation:

• The molecular formula of acetophenone is C₈H₈O.
• The molar mass of acetophenone is calculated as follows:
• Carbon (C): 8 × 12 = 96 g/mol
• Hydrogen (H): 8 × 1 = 8 g/mol
• Oxygen (O): 1 × 16 = 16 g/mol
• Total molar mass = 96 + 8 + 16 = 120 g/mol
• The percentage by mass of hydrogen is:

Percentage of H = (8/120) × 100 = 6.7%

• A. 6.7%.

Question 2

Question: Which statement is correct?

Options:
A. 1.0 g of hydrogen gas contains 3.0×10²³ atoms
B. 4.0 g of helium gas contains 1.2×10²⁴ atoms
C. 16 g of methane gas contains 3.0×10²⁴ atoms
D. 44 g of carbon dioxide gas contains 6.0×10²³ atoms

Answer: C. 16 g of methane gas contains 3.0×10²⁴ atoms

Explanation:

We use:

• 1 mole = 6.02 × 10²³ atoms/molecules

Let’s check:

• A: 1.0 g H = 1/1 = 1 mol → 6.02×10²³ atoms ❌
• B: 4.0 g He = 4/4 = 1 mol → 6.02×10²³ atoms ❌
• C: 16 g CH₄ = 16/16 = 1 mol → 6.02×10²³ molecules = 5 atoms × 6.02×10²³ = 3.01×10²⁴ atoms ✅
• D: 44 g CO₂ = 1 mol = 6.02×10²³ molecules ❌

✅ Answer: C

          

Question 3

Question: When 0.42 g of propanol reacts with excess sodium, hydrogen gas is produced. What volume of hydrogen, measured at room temperature and pressure, is produced?

Options:
A. 84 cm³
B. 168 cm³
C. 252 cm³
D. 336 cm³

Answer: A. 84 cm³

Explanation:

0.42 g propanol + Na → H₂ gas. What volume of H₂ at RTP?

Propanol: C₃H₇OH, reacts:
C₃H₇OH + Na → C₃H₇ONa + ½H₂

Molar mass of C₃H₇OH = 60 g/mol
Moles = 0.42 / 60 = 0.007 mol
Moles H₂ = 0.007 × ½ = 0.0035 mol
Volume at RTP = 0.0035 × 24,000 = 84 cm³

✅ Answer: A

         

Question 4

Question: Permanent hard water may contain dissolved magnesium sulfate, MgSO₄​. How many electrons are present in a sulfate anion?

Options:
A. 46
B. 48
C. 49
D. 50

Answer: D. 50

Explanation:

• The sulfate anion (SO₄²⁻​) has:
• Sulfur (S): 16 electrons
• Oxygen (O): 4 × 8 = 32 electrons
• +2 extra e⁻ (due to charge)
• Total electrons = 16 + 32 + 2 = 50 electrons (including the 2 extra electrons from the charge).

The correct answer is D. 50.

            

Question 5

Question: Three orbitals j, k and l are shown. What is the name of j, k and l?

Options:
A. Px, Py, Pz​
B. s, Pz, Py​
C. s, Px, Pz​
D. s, Px, Py​

Answer: D. s, Px, Py​

Explanation: 

The s-orbital is spherical, while the pp-orbitals are dumbbell-shaped and oriented along the x, y, and z axes.

• Based on the diagram, j is the s-orbital, k is the Px​-orbital, and l is the Py​-orbital.

Only s-orbital is spherical, others are dumbbell-shaped on x, y, z axes.

• j = s
• k = px
• l = py

The correct answer is D. s, Px, Py​.

            

Question 6

Question: The electronic configuration of an ion is 1s²2s²2p⁶3s²3p⁶3d³. What is this ion?

Options:
A. Cr³⁺
B. Fe³⁺
C. Ni²⁺
D. Ti²⁺

Answer: A. Cr³⁺

Explanation:

Electronic config: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d³ → total 21 e⁻

• Cr: atomic no. 24 → Cr³⁺ = 21 e⁻ ✅

✅ Answer: A

         

Question 7

Question: What are the shapes of the molecules of methane and sulfur hexafluoride?

Options:
A. pyramidal, trigonal
B. pyramidal, octahedral
C. tetrahedral, trigonal
D. tetrahedral, octahedral

Answer: D. tetrahedral, octahedral

Explanation:

• Methane (CH₄​) has a tetrahedral shape due to sp³ hybridization (4 bond pairs, no lone pairs)
• Sulfur hexafluoride (SF₆​) has an octahedral shape due to sp³d² hybridization (6 bond pairs)
• The correct answer is D. tetrahedral, octahedral.

     

Question 8

Question: Which molecule has no overall dipole?

Options:
A. CH_4​
B. HCl
C. H_2​O
D. NH₃​

Answer: A. CH_4​

Explanation:

• CH₄​ is a symmetrical molecule with no net dipole moment, non-polar ✅
• HCl, H_2​O, and NH_3​ all have net dipole moments (polars) due to their asymmetrical shapes.
• The correct answer is A. CH₄​.

         

Question 9

Question: Which compound has the highest boiling point and what is the intermolecular force that causes this boiling point to be the highest?

Options:
A. ethanol, hydrogen bonds
B. chloromethane, permanent dipole
C. methane, Van der Waals
D. methane, hydrogen bonds

Answer: A. ethanol, hydrogen bonds

Explanation:

Highest boiling point & reason?

• Ethanol has hydrogen bonding → strongest intermolecular force
• Others: van der Waals or dipole only

• Ethanol (C₂H₅OH) has hydrogen bonding, which is the strongest intermolecular force, leading to the highest boiling point.
• The correct answer is A. ethanol, hydrogen bonds.

         

Question 10

Question: “A lattice of positive ions surrounded by delocalised electrons.” Which type of bonds does the statement best describe?

Options:
A. co-ordinate bonds
B. covalent bonds
C. ionic bonds
D. metallic bonds

Answer: D. metallic bonds

Explanation:

• Metallic bonds involve a lattice of positive ions surrounded by a sea of delocalized electrons.
• The correct answer is D. metallic bonds.

       

Question 11

Question: The gas laws can be summarised in the ideal gas equation. A certain gas of mass 7.20 g is contained in a tank of volume 5.00 dm33 at a pressure of 135 kPa and temperature of 42.5 °C. Assume that the gas behaves as an ideal gas. What is the molar mass, Mr​, of the gas in the tank?

Options:
A. 1.85 g mol⁻¹
B. 3.77 g mol⁻¹

C. 28.0 g mol⁻¹

D. 35.8 g mol⁻¹

Answer: D. 35.8 g mol⁻¹

Explanation:

Use ideal gas equation to calculate molar mass (Mᵣ):
pV = nRT ⇒    n  =  pV/RT     ⇒  M_r  = mass / number of moles     

Given:

• p = 135 kPa = 135,000 Pa
• V = 5.00 dm³ = 0.005 m³
• T = 42.5 °C = 315.5 K
• R = 8.31 J mol⁻¹K⁻¹
• mass = 7.20 g

n =  135 000 x 0.005 / 8.31 x 315.5  =  675/ 2622.4045    ≈ 0.2575 mol

            M_r  ⇒ 7.20 / 0.2575 ≈ 28.0​

✅ Answer: C

          

Question 12

Question: Which equation represents the standard enthalpy change of formation of ethanol?

Options:
A. 2C(s)+3H₂(g)+1/2O₂(g)→C₂H₅OH(g)
B. 2C(s)+3H₂(g)+1/2O₂(g)→C₂H₅OH(l)
C. 4C(s)+6H₂(g)+O₂(g)→2C₂H₅OH(g)
D. 4C(s)+6H₂(g)+O₂(g)→2C₂H₅OH(l)

Answer: B. 2C(s) + 3H₂(g) + 1/2O₂(g) → C₂H₅OH(l)

Explanation:

• The standard enthalpy change of formation refers to the formation of 1 mole of a compound from its elements in their standard states.
• The correct equation is B, as it represents the formation of 1 mole of ethanol in its liquid state.

         

Question 13

Question: A reaction pathway is shown. Which row is correct?

Options:
A. Q, U
B. Q, S
C. R, S
D. T, U

Answer: B. Q, S

Explanation:

• The enthalpy change of the forward reaction is represented by Q.
• The activation energy of the reverse reaction is represented by S.
• The correct answer is B. Q, S.

          

Question 14

Question: The equation for the complete combustion of methanol is shown. What is the enthalpy change of combustion of methanol?

Options:
A. −966 kJ mol⁻¹
B. −732 kJ mol⁻¹
C. −234 kJ mol⁻¹
D. +732 kJ mol⁻¹

Answer: B. −732 kJ mol⁻¹

Explanation:

• Using Hess's Law, the enthalpy change of combustion is:

• ΔH_c=ΔH_f(products)−ΔH_f(reactants)

  ΔH_c = [(−394) + 2(−286)] − (−234) = −732 kJ mol⁻¹

• The correct answer is B. −732 kJ mol⁻¹.

         

Question 15

Question: The reaction between acidified potassium manganate(VII) ions, MnO₄⁻​, and aqueous Fe²⁺ results in the manganate(VII) ions being reduced to manganese(II) ions, Mn²⁺. What is the correct equation for this reaction?

Options:
A. Fe²⁺ + MnO₄⁻+ 8H⁺→ Fe³⁺+Mn²⁺+4H₂O
B. 2Fe²⁺ + MnO4⁻+ 8H⁺→ 2Fe³⁺+Mn²⁺+4H₂O
C. 10Fe²⁺ + MnO₄⁻+ 8H⁺→ 10Fe³⁺+Mn²⁺+4H₂O
D. 5Fe²⁺ + MnO₄⁻+ 8H⁺ → 5Fe³⁺+Mn²⁺+4H₂O

Answer: D. 5Fe²⁺+   MnO₄⁻+8H⁺→5Fe³⁺+ Mn²⁺+4H₂O

Explanation:

Redox reaction: MnO₄⁻ oxidises Fe²⁺ to Fe³⁺.

• The balanced redox equation is:

5Fe²⁺+ MnO₄⁻+ 8H⁺ → 5Fe³⁺+ Mn²⁺+ 4H₂O

The correct answer is D.

            

Question 16

Question: Which reaction is not a redox reaction?

Options:
A. 2Ca + O₂ →2CaO₂
B. Ca+2H₂O→Ca(OH)₂+H_2​
C. CaCO₃→CaO+CO_2​
D. 2Ca(NO₃)₂→2CaO+4NO₂+O₂​

Answer: C. CaCO₃→CaO+CO₂

Explanation:

Redox: look for change in oxidation number.

• In reaction C, CaCO₃ → CaO + CO₂
  there is no change in oxidation states of any element, so it is not a redox reaction.

·        Ca stays +2, C stays +4, O stays −2 → no redox

The correct answer is C.

           

Question 17

Question: Concentrated aqueous copper(II) sulfate is electrolysed using copper electrodes. Which ionic half-equation describes the reaction taking place at the cathode?

Options:
A. 2H⁺+2e⁻→ H₂
B. 4OH⁻→2H₂O + O₂ + 4e⁻
C. Cu → Cu²⁺+ 2e⁻
D. Cu²⁺+2e⁻→ Cu

Answer: D. Cu²⁺+2e⁻→ Cu

Explanation:

• Electrolysis of CuSO₄ using copper electrodes (Cu²⁺ gains electrons):
• At the cathode, reduction occurs, and Cu²⁺ ions are reduced to Cu.
• The correct answer is D.

           

Question 18

Question: The reaction between hydrogen and chlorine is reversible. Which conditions of concentration and temperature favour the forward reaction?

Options:
A. add some hydrogen chloride, decrease the temperature
B. add some hydrogen chloride, increase the temperature
C. remove some hydrogen chloride, decrease the temperature
D. remove some hydrogen chloride, increase the temperature

Answer: D. remove some hydrogen chloride, increase the temperature.

Explanation:

• According to Le Chatelier's principle, removing HCl (a product) and increasing the temperature (since the reaction is endothermic) will favour the forward reaction.

H₂​  +  Cl_2​ ⇌ 2HCl                   ∆H = + 49.7 (endothermic)

Favour forward reaction by:

• removing product (HCl)
• increasing temperature
• The correct answer is D.

         

Question 19

Question: The table shows the concentration in an equilibrium mixture by the Contact process. What is the value and the unit of the equilibrium constant, K_p​?

Options:
A. 0.1 mol dm⁻³
B. 10 mol⁻¹ dm³
C. 20 mol dm⁻³
D. 20 mol⁻¹ dm³

Answer: D. 20 mol⁻¹ dm³

Explanation:

• The equilibrium constant K_p​ is calculated as:

Kp = [SO₃]² / [SO₂]²[O₂]  = 0.8² / 0.4² x 0.2   = 20 mol⁻¹ dm³

Units: (mol/dm³)²/((mol/dm³)²×mol/dm³) = mol⁻¹dm³

✅ Answer: D

• The correct answer is D.

           

Question 20

Question: Ammonia is manufactured from hydrogen and nitrogen using the Haber process. Which expression for equilibrium constant in terms of partial pressures, Kp​, is correct?

Options:
A. (pNH₃)²/(pH₂)³  × (pN₂)​
B. (pNH₃)²/(pH₂)³  + (pN₂)​
C. 2(pNH₃)/3(pH₂)³ × (pN₂)​
D. 2(pNH₃)³/(pH₂) × (pN₂)​

Answer: A. (pNH₃)²/(pH₂)³ × (pN₂)​

Explanation:

• The equilibrium constant K_p​ for the Haber process is:

                _Kp=(pNH₃)²/(pH₂)³ × (pN₂)​

• The correct answer is A.

              

Question 21

Question: The equation shows the reaction of sodium chloride with concentrated sulfuric acid. Which one is the conjugate base for the forward reaction?

Options:
A. Cl⁻
B. HCl
C. HSO₄⁻​
D. H_2​SO_4​

Answer: C. HSO₄⁻​

Explanation:

• In the forward reaction, H_2​SO_4​ donates a proton (H⁺) to Cl⁻, forming HCl and HSO₄⁻​.
• H₂SO₄ donates a proton → conjugate base is what remains → HSO₄⁻.
• The conjugate base of H_2​SO₄​ is HSO₄⁻​.

The correct answer is C.

          

Question 22

Question: Two reactions are shown. Both reactions use catalysts. Which statement about the catalysts is correct?

Options:
A. Both reactions use a heterogeneous catalyst.
B. Both reactions use a homogeneous catalyst.
C. Reaction 1 uses a heterogeneous catalyst and reaction 2 uses a homogeneous catalyst.
D. Reaction 1 uses a homogeneous catalyst and reaction 2 uses a heterogeneous catalyst.

Answer: A. Reaction 1 uses a heterogeneous catalyst and reaction 2 uses a heterogeneous catalyst.

Explanation:

• Reaction 1 (Contact process) uses a heterogeneous catalyst (vanadium(V) oxide).
• Reaction 2 (Haber process) uses a heterogeneous catalyst (iron).
• Contact process (SO₃): solid V₂O₅ → heterogeneous
• Haber process (NH₃): iron solid → heterogeneous

✅ Answer: A

          

Question 23

Question: The Boltzmann distribution shows the distribution of the kinetic energy of molecules at a constant temperature. The temperature is increased by 10K. Which row is correct?

Options:
A. the peak is at a lower height, size of the area labelled Y decreases
B. the peak is at a lower height, size of the area labelled Y increases
C. the peak remains the same height, size of the area labelled Y decreases
D. the peak remains the same height, size of the area labelled Y increases

Answer: B. the peak is at a lower height, size of the area labelled Y increases

Explanation:

• When temperature increases, the peak of the Boltzmann distribution shifts to a lower height, and the area under the curve (Y) increases.

Boltzmann distribution: increasing T → curve flattens, peak shifts right

So:

• peak is lower
• area Y (Ea) increase
• The correct answer is B.

           

Question 24

Question: Which property is shown in graph S and graph T?

Options:
A. melting point, ionisation energy
B. melting point, atomic radius
C. atomic radius, melting point
D. ionisation energy, electronegativity

Answer: B. melting point, atomic radius

Explanation:

• Graph S shows melting point, and graph T shows atomic radius.
• The correct answer is B.

         

Question 25

Question: Which period 3 chloride dissolves in water and gives a solution of pH 7?

Options:
A. Al₂​Cl₆​
B. PCl₅​
C. NaCl
D. SiCl_4​

Answer: C. NaCl

Explanation:

• NaCl is a neutral salt that dissolves in water to give a solution with pH 7.
• The correct answer is C.

          

Question 26

Question: An aqueous solution contains both barium and calcium ions. Aqueous sodium hydroxide and dilute sulfuric acid are added to separate portions of this solution. Which row shows the precipitate formed?

Options:
A. barium hydroxide, barium sulfate
B. barium hydroxide, calcium sulfate
C. calcium hydroxide, barium sulfate
D. calcium hydroxide, calcium sulfate

Answer: C. calcium hydroxide, barium sulfate

Explanation:

• NaOH reacts with Ca²⁺ to form Ca(OH)₂​ (calcium hydroxide), which is insoluble.
• H₂​SO_4​ reacts with Ba²⁺ to form BaSO_4​ (barium sulfate), which is insoluble.

·        OH⁻: both Ba²⁺ and Ca²⁺ form precipitates of hydroxides

·        H₂SO₄: Ba²⁺ forms insoluble BaSO₄, CaSO₄ is more soluble

The correct answer is C.

          

Question 27

Question: A sample of zinc nitrate is heated in the apparatus as shown. A mixture of gases is released. The mixture is then tested with a glowing splint. What are the results?

Options:
A. colourless, extinguished
B. brown, extinguished
C. colourless, relights
D. brown, relights

Answer: D. brown, relights

Explanation:

• When zinc nitrate is heated, it decomposes to produce NO₂​ (brown gas) and O₂​ (colourless gas).
• The glowing splint relights in the presence of O₂​.

            Zinc nitrate decomposes → ZnO (solid) + NO₂ (brown) + O₂

• Brown gas
• Oxygen supports glowing splint → relights
• The correct answer is D.

             

Question 28

Question: The Group 17 elements chlorine, bromine and iodine have different colours. Which row shows the correct colour of the Group 17 elements when in a vapour state?

Options:
A. green, purple, red-brown
B. green, red-brown, purple
C. purple, red-brown, green
D. red-brown, green, purple

Answer: B. green, red-brown, purple

Explanation:

• Chlorine gas is green, bromine vapour is red-brown, and iodine vapour is purple.

The correct answer is B.

            

Question 29

Question: What happens when chlorine is bubbled through aqueous potassium iodide?

Options:
A. Iodide ions are oxidised to iodine.
B. Chlorine is oxidised to chlorate(V) ions.
C. Chlorine is oxidised to chloride ions.
D. There is no observable reaction.

Answer: A. Iodide ions are oxidised to iodine.

Explanation:

• Chlorine is more reactive than iodine and will oxidise iodide ions (I⁻) to iodine (I₂​).

·        Cl₂ is more reactive → displaces I₂:

·        Cl₂ +  2I⁻ → 2Cl⁻ + I₂​

·        I⁻ is oxidised to I₂.

• The correct answer is A.

            

Question 30

Question: Chlorine reacts with hot concentrated sodium hydroxide solution to produce sodium chloride, another chlorine containing compound and water. Which row is correct for this reaction?

Options:
A. 1, 1, NaOCl
B. 2, 3, NaOCl₂​
C. 3, 5, NaOCl₃
D. 3, 6, NaOCl₃

Answer: A. 1, 1, NaOCl

Explanation:

• The reaction is:

Cl₂   +  NaOH   →   NaCl  +  NaOCl  +   H₂O

So: 1 mol Cl₂   ​→  1 mol NaCl (Balanced Equation)

• 1 mole of Cl₂​ produces 1 mole of NaCl and 1 mole of NaOCl.
• The correct answer is A.

           

Question 31

Question: The atmosphere contains several pollutants. Which gas causes acid rain if it is released into the air and causes breathing difficulties?

Options:
A. carbon dioxide
B. carbon monoxide
C. nitrogen
D. sulfur dioxide

Answer: D. sulfur dioxide

Explanation:

• Sulfur dioxide (SO₂​) reacts with water in the atmosphere to form sulfuric acid, causing acid rain. It also causes breathing difficulties. SO₂ forms acid rain and causes respiratory issues
• The correct answer is D.

             

Question 32

Question: There is a change in the oxidation number of nitrogen in the nitrogen cycle in terms of the ions and molecules involved. Which row shows the correct oxidation number of nitrogen?

Options:
A. -3, +5
B. -3, +1
C. +1, -3
D. +5, +1

Answer: A. -3, +5

Explanation:

• In ammonia (NH₃​), nitrogen has an oxidation number of -3.
• In nitrate ions (NO₃⁻​), nitrogen has an oxidation number of +5.
• The correct answer is A.

            

Question 33

Question: What is the monomer unit for PVC?

Options:
A. chloroethene
B. ethene
C. propene
D. tetrafluoroethene

Answer: A. chloroethene

Explanation:

• PVC (polyvinyl chloride) is made from the monomer chloroethene (CH₂​=CHCl).
• The correct answer is A.

            

Question 34

Question: A reaction occurs when a sample of 2-bromopropane is heated under reflux with potassium hydroxide dissolved in ethanol. Which row is correct?

Options:
A. elimination, propan-1-ol
B. elimination, propene
C. substitution, propan-1-ol
D. substitution, propene

Answer: B. elimination, propene

Explanation:

• Heating 2-bromopropane with KOH in ethanol leads to an elimination reaction, producing propene.
• 2-bromopropane + KOH (ethanol) → elimination → alkene (propene)
• The correct answer is B.

            

Question 35

Question: When an organic compound F is treated with hot aqueous acid, two compounds are formed. Which two structures show the compounds formed?

Options:
A. CH₃CH₂CO₂H+CH₃CH₂CH₂OH
B. (CH₃)₂CHCO₂H+CH₃CH₂CH₂OH
C. CH₃CH₂CO₂H+CH₃CH(OH)CH_3​
D. (CH₃)₂CHCO₂H+CH₃CH(OH)CH_3​

Answer: C. CH₃CH₂CO₂H+CH₃CH(OH)CH₃​

Explanation:

• The compound CH₃CH₂CO₂CH(OH)₂​ undergoes hydrolysis to form propanoic acid (CH₃CH₂CO₂H) and isopropanol (CH₃CH(OH)CH₃).

CH₃CH₂CO₂CH(CH₃)₂ is an ester → acid hydrolysis gives:

• acid: CH₃CH₂COOH
• alcohol: CH₃CH(OH)CH₃
• The correct answer is C.

            

Question 36

Question: Which compound does not show geometrical isomerism?

Options:
A. CBr(CH₃)=CH_2​
B. CBr(CH₃)=CBr(CH₃)
C. CH(CH₃)=CH(CH₂CH₃)
D. CH(CH₃)=CH(CH₂CH₂CH₃)

Answer: A. CBr(CH₃)=CH_2​

Explanation:

• Geometrical isomerism requires two different groups on each carbon of the double bond. CBr(CH₃)=CH₂​ does not meet this requirement.

Geometrical isomerism needs C=C with different groups

• A: CH₂=C(CH₃)Br → only 1 H → no cis-trans
• B: CBr(CH₃)=CBr(CH₃) → has cis-trans
• C: CH(CH₃)=CH(CH₂CH₃) → yes
• D: yes
• The correct answer is A.

             

Question 37

Question: How many chain isomers have the molecular formula C₄H₁₀​?

Options:
A. 2
B. 3
C. 5
D. 6

Answer: A. 2

Explanation:

• C₄H₁₀​ has two chain isomers: butane and 2-methylpropane.
• The correct answer is A.

            

Question 38

Question: The molecular formula of compound Y is C₆H₁₄O. Compound Y can react with alkaline aqueous iodine to form tri-iodomethane. What could be the identity of compound Y?

Options:
A. CH₃CH₂CH₂COH(CH₃)₂​
B. CH₂(OH)CH₂CH(CH₃)_2​
C. CH₃CH₂CH(OH)CH(CH₃)₂​
D. CH₃CH₂CH(CH₃)CH₂CH₂OH

Answer: C. CH₃CH₂CH(OH)CH(CH₃)₂​

Explanation:

• The iodoform test is positive for compounds with the structure CH₃CH(OH)R.
• Triiodomethane test → needs CH₃CO– or CH₃CH(OH)–
  Only option C has a secondary alcohol with CH₃–C(OH)–
• The correct answer is C.

             

Question 39

Question: Which types of stereoisomerism are shown by 1,2-dichloroethene?

Options:
A. both geometrical and optical isomerism
B. geometrical isomerism only
C. neither geometrical isomerism nor optical isomerism
D. optical isomerism only

Answer: B. geometrical isomerism only

Explanation:

• 1,2-dichloroethene can exhibit geometrical isomerism (cis/trans) but not optical isomerism (no chiral center). 
• The correct answer is B.

             

Question 40

Question: Aldehydes and ketones are produced by the oxidation of either primary or secondary alcohols. Which row is correct?

Options:
A. aldehydes, ketones
B. ketones, aldehydes
C. aldehydes, aldehydes and ketones
D. ketones, aldehydes and ketones

Answer: A. aldehydes, ketones

Explanation:

• Primary alcohols oxidise to aldehydes, and secondary alcohols oxidise to ketones.

·        Primary alcohol → aldehyde → carboxylic acid

·        Secondary alcohol → ketone only

The correct answer is A.

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