Electrolysis, Electrolytes, Electrodes and Industrial Applications

1. Which statement correctly describes an electrolyte?

A a substance that conducts electricity because electrons move through it
B a substance that conducts electricity when molten or aqueous because ions move
C a substance that conducts electricity only when solid
D a substance that is always decomposed by heat

2. Molten lead(II) bromide is electrolysed using inert electrodes.

Which row is correct?

	cathode product	anode product
A	lead	bromine
B	bromine	lead
C	hydrogen	bromine
D	lead	oxygen

3. Why does solid lead(II) bromide not conduct electricity?

A It contains no ions.
B Its ions are fixed in position.
C Its electrons are shared between atoms.
D Its ions are neutral.

4. Which statement about electrolysis is correct?

A Oxidation occurs at the cathode.
B Reduction occurs at the anode.
C Cations move towards the cathode.
D Anions gain electrons at the anode.

5. During electrolysis of molten aluminium oxide, Al2O3, what is discharged at the cathode?

A Al3+ ions gain electrons to form aluminium.
B O2– ions lose electrons to form oxygen.
C Al3+ ions lose electrons to form aluminium.
D O2– ions gain electrons to form oxygen.

6. Which half-equation represents the reaction at the cathode during electrolysis of molten sodium chloride?

A Na+ + e– → Na
B Na → Na+ + e–
C 2Cl– → Cl2 + 2e–
D Cl2 + 2e– → 2Cl–

7. Which half-equation represents the reaction at the anode during electrolysis of molten magnesium chloride?

A Mg2+ + 2e– → Mg
B Mg → Mg2+ + 2e–
C 2Cl– → Cl2 + 2e–
D Cl2 + 2e– → 2Cl–

8. Aqueous copper(II) sulfate is electrolysed using inert platinum electrodes.

Which products are formed?

	cathode	anode
A	copper	oxygen
B	hydrogen	oxygen
C	copper	sulfur dioxide
D	hydrogen	sulfur trioxide

9. Aqueous copper(II) sulfate is electrolysed using copper electrodes.

Which statement is correct?

A Copper is deposited at the cathode and oxygen forms at the anode.
B Copper dissolves from the anode and copper deposits at the cathode.
C Hydrogen forms at the cathode and oxygen forms at the anode.
D The solution becomes colourless because sulfate ions are discharged.

10. During electrolysis of aqueous copper(II) sulfate using copper electrodes, what happens to the concentration of copper(II) ions in solution?

A It increases steadily.
B It decreases steadily.
C It stays approximately constant.
D It becomes zero immediately.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

11. In copper purification, which electrode is made from impure copper?

A cathode only
B anode only
C both cathode and anode
D neither cathode nor anode

12. In copper purification, which statement is correct?

A Pure copper forms at the anode.
B Impurities from the cathode fall as anode sludge.
C Copper atoms from the impure anode form Cu2+ ions.
D Sulfate ions are discharged to make sulfur dioxide.

13. In electroplating a steel spoon with silver, which arrangement is correct?

A spoon as anode, silver as cathode, silver nitrate solution
B spoon as cathode, silver as anode, silver nitrate solution
C spoon as cathode, graphite as anode, sodium chloride solution
D spoon as anode, graphite as cathode, silver nitrate solution

14. Why must the object to be electroplated be connected to the negative terminal?

A Metal atoms must lose electrons at the object.
B Metal ions must gain electrons at the object.
C Non-metal ions must be oxidised at the object.
D The object must dissolve into the electrolyte.

15. Which condition gives the most even metal coating during electroplating?

A very high current and dirty object
B low steady current and clean object
C no electrolyte and high voltage
D reactive anode and no metal ions in solution

16. Concentrated aqueous sodium chloride is electrolysed using inert electrodes.

Which products are made?

	cathode	anode	remaining solution
A	sodium	chlorine	water
B	hydrogen	chlorine	sodium hydroxide
C	hydrogen	oxygen	sodium chloride
D	sodium	oxygen	hydrochloric acid

17. Dilute aqueous sodium chloride is electrolysed using inert electrodes.

Which products are most likely at the electrodes?

	cathode	anode
A	sodium	chlorine
B	hydrogen	oxygen
C	sodium	oxygen
D	hydrogen	chlorine only

18. Why is hydrogen produced instead of sodium during electrolysis of aqueous sodium chloride?

A Sodium ions cannot move in solution.
B Hydrogen ions/water are more easily reduced than sodium ions.
C Sodium is less reactive than hydrogen.
D Sodium ions are negative and move to the anode.

19. In concentrated aqueous sodium chloride, why is chlorine produced at the anode instead of oxygen?

A Chloride ions are present in high concentration and are discharged.
B Hydroxide ions cannot move to the anode.
C Oxygen is produced only from molten salts.
D Chlorine is produced at the cathode, not the anode.

20. Which ion is discharged at the cathode during electrolysis of aqueous silver nitrate using inert electrodes?

A Ag+
B H+
C NO3–
D OH–

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

21. Aqueous potassium iodide is electrolysed using inert electrodes.

Which products are expected?

	cathode	anode
A	potassium	iodine
B	hydrogen	iodine
C	hydrogen	oxygen
D	potassium	oxygen

22. Aqueous potassium sulfate is electrolysed using inert electrodes.

Which products are formed?

	cathode	anode
A	potassium	sulfur dioxide
B	hydrogen	oxygen
C	potassium	oxygen
D	hydrogen	sulfur

23. Which aqueous solution produces oxygen at the anode when electrolysed using inert electrodes?

A concentrated sodium chloride
B copper(II) chloride
C dilute sulfuric acid
D potassium bromide

24. Which aqueous solution produces a metal at the cathode when electrolysed using inert electrodes?

A sodium sulfate
B potassium nitrate
C copper(II) sulfate
D magnesium chloride

25. Aqueous zinc sulfate is electrolysed using inert electrodes.

Which cathode product is most likely at O Level?

A zinc
B hydrogen
C sulfur
D oxygen

26. Aqueous silver nitrate is electrolysed using inert electrodes.

Which statement is correct?

A Silver ions are reduced at the cathode.
B Nitrate ions are oxidised at the anode.
C Silver atoms are oxidised at the cathode.
D Hydrogen is always produced instead of any metal.

27. Which anion is most likely discharged at the anode from concentrated aqueous sodium bromide?

A Na+
B Br–
C H+
D OH–

28. During electrolysis, which statement about electron flow is correct?

A Electrons move through the electrolyte from cathode to anode.
B Electrons enter the cathode from the power supply.
C Electrons leave the cathode and enter the solution.
D Electrons are carried through solution by sulfate ions.

29. What occurs at the positive electrode during electrolysis?

A positive ions gain electrons
B negative ions lose electrons
C positive ions lose electrons
D negative ions gain electrons

30. Which row correctly links electrode and process?

	cathode	anode
A	oxidation	reduction
B	reduction	oxidation
C	oxidation	oxidation
D	reduction	reduction

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

31. A student electrolyses molten zinc chloride.

Which statement is correct?

A Zinc forms at the anode and chlorine forms at the cathode.
B Zinc forms at the cathode and chlorine forms at the anode.
C Hydrogen forms at the cathode and oxygen forms at the anode.
D Zinc chloride does not conduct when molten.

32. A student electrolyses aqueous zinc chloride using inert electrodes.

Which pair of products is most likely?

A zinc and chlorine
B hydrogen and chlorine
C zinc and oxygen
D hydrogen and oxygen only

33. What is the key difference between electrolysis of molten sodium chloride and aqueous sodium chloride?

A Molten sodium chloride gives hydrogen at the cathode.
B Aqueous sodium chloride can give hydrogen at the cathode because water is present.
C Molten sodium chloride gives oxygen at the anode.
D Aqueous sodium chloride cannot conduct electricity.

34. Cryolite is used in the extraction of aluminium.

What is its main purpose?

A to increase the melting point of aluminium oxide
B to lower the melting point and dissolve aluminium oxide
C to react with oxygen to produce carbon dioxide
D to form aluminium ions from aluminium atoms

35. Why are graphite anodes replaced regularly during aluminium extraction?

A Aluminium reacts with graphite to form aluminium carbide only.
B Oxygen produced at the anode reacts with carbon to form carbon dioxide.
C Sodium ions react with graphite to form sodium carbide.
D Graphite dissolves in molten aluminium oxide without reaction.

36. Which half-equation occurs at the anode during aluminium extraction?

A Al3+ + 3e– → Al
B Al → Al3+ + 3e–
C 2O2– → O2 + 4e–
D O2 + 4e– → 2O2–

37. Which overall change happens to aluminium ions during extraction?

A They are oxidised by losing electrons.
B They are reduced by gaining electrons.
C They are oxidised by gaining oxygen.
D They are reduced by losing oxygen.

38. Why is aluminium extraction expensive?

A Aluminium oxide is rare and impossible to melt.
B Large amounts of electricity are needed.
C Aluminium is extracted using carbon in a blast furnace.
D Aluminium is found only as the free metal.

39. Which substance is the electrolyte in the industrial extraction of aluminium?

A molten aluminium only
B molten cryolite with dissolved aluminium oxide
C aqueous aluminium chloride
D solid aluminium oxide

40. Which statement about aluminium extraction is correct?

A Aluminium forms at the positive electrode.
B Oxygen forms at the negative electrode.
C Aluminium forms at the cathode.
D Cryolite is reduced to aluminium.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

41. A solution contains Cu2+, Na+, SO4 2– and Cl– ions. It is electrolysed using inert electrodes and the chloride ion concentration is high.

Which products are most likely?

	cathode	anode
A	sodium	oxygen
B	copper	chlorine
C	hydrogen	oxygen
D	copper	sulfur dioxide

42. A solution contains Cu2+, H+, NO3– and OH– ions and is electrolysed using inert electrodes.

Which product forms at the cathode first?

A copper
B hydrogen
C nitrogen dioxide
D oxygen

43. A solution contains only K+, H+, SO4 2– and OH– ions.

Which products are formed during electrolysis using inert electrodes?

A potassium and sulfur dioxide
B potassium and oxygen
C hydrogen and oxygen
D hydrogen and sulfur

44. A metal object is copper-plated using copper(II) sulfate solution and a copper anode.

Which change occurs at the anode?

A Cu2+ + 2e– → Cu
B Cu → Cu2+ + 2e–
C 2OH– → O2 + 2H2O + 4e–
D SO4 2– → SO4 + 2e–

45. A student electrolyses aqueous copper(II) chloride using inert electrodes.

Which statement is correct?

A Copper forms at the cathode and chlorine forms at the anode.
B Hydrogen forms at the cathode and oxygen forms at the anode.
C Copper forms at the anode and chlorine forms at the cathode.
D Hydrogen forms at the cathode and chlorine forms at the anode.

46. During electrolysis of aqueous copper(II) chloride using inert electrodes, why does the blue-green colour fade?

A Copper(II) ions are removed from solution at the cathode.
B Chloride ions turn colourless at the cathode.
C Copper atoms dissolve at the anode.
D Hydrogen ions increase in concentration.

47. Aqueous sodium sulfate is electrolysed using inert electrodes.

What happens to the concentration of sodium sulfate during electrolysis if water is decomposed?

A It decreases because sodium ions are discharged.
B It increases because water is removed as gases.
C It becomes zero because sulfate ions are discharged.
D It stays exactly constant because no gases form.

48. In electrolysis, which species migrates to the anode?

A cations only
B anions only
C electrons in solution only
D neutral atoms only

49. Which pair of substances would both conduct electricity?

A solid sodium chloride and solid copper
B molten sodium chloride and solid copper
C solid sugar and ethanol
D solid lead(II) bromide and solid sulfur

50. Aqueous nickel(II) sulfate is used to nickel-plate a steel object. Which arrangement is correct?

A steel object as anode, nickel as cathode
B steel object as cathode, nickel as anode
C steel object as cathode, graphite as electrolyte
D nickel sulfate as cathode, nickel as electrolyte

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

1. B

A wrong: This describes metallic conduction, not an electrolyte.
B right: Electrolytes conduct when molten or aqueous because mobile ions carry charge.
C wrong: Ionic solids usually do not conduct when solid.
D wrong: Electrolytes are decomposed by electricity, not always by heat.

2. A

A right: Molten PbBr2 contains Pb2+ and Br– ions. Pb2+ gains electrons at cathode to form lead; Br– loses electrons at anode to form bromine.
B wrong: Products are reversed.
C wrong: Hydrogen is not present in molten lead(II) bromide.
D wrong: Oxygen is not present.

3. B

A wrong: Solid lead(II) bromide contains ions.
B right: Its ions are fixed in position and cannot move to carry charge.
C wrong: It is ionic, not covalent.
D wrong: Ions are charged, not neutral.

4. C

A wrong: Oxidation occurs at the anode.
B wrong: Reduction occurs at the cathode.
C right: Cations are positive ions, so they move towards the negative cathode.
D wrong: Anions lose electrons at the anode.

5. A

A right: Al3+ ions gain electrons at the cathode: Al3+ + 3e– → Al.
B wrong: This happens at the anode.
C wrong: Gaining electrons forms aluminium, not losing electrons.
D wrong: Oxide ions lose electrons, not gain them.

6. A

A right: Sodium ions gain electrons at the cathode to form sodium metal.
B wrong: This is oxidation of sodium, not cathode reduction.
C wrong: This is the anode reaction.
D wrong: This is reduction of chlorine, not the molten sodium chloride cathode reaction.

7. C

A wrong: This is cathode reduction of magnesium ions.
B wrong: Magnesium atoms are not oxidised at the anode here.
C right: Chloride ions lose electrons at the anode: 2Cl– → Cl2 + 2e–.
D wrong: This is reduction of chlorine, not anode oxidation.

8. A

A right: Cu2+ is reduced to copper at the cathode; OH–/water forms oxygen at the anode.
B wrong: Copper forms instead of hydrogen at the cathode.
C wrong: Sulfate ions are not discharged to form sulfur dioxide.
D wrong: Neither product pair is correct.

9. B

A wrong: Oxygen forms with inert electrodes, not copper anodes.
B right: Copper dissolves from the anode as Cu2+ and copper deposits at the cathode.
C wrong: Copper is deposited instead of hydrogen.
D wrong: Sulfate ions are spectators.

10. C

A wrong: Copper ions are not only being produced.
B wrong: Copper ions are not only being removed.
C right: Cu2+ ions lost at cathode are replaced by Cu2+ ions formed at copper anode, so concentration stays approximately constant.
D wrong: It does not become zero.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

11. B

A wrong: The cathode is pure copper.
B right: The impure copper is the anode so it dissolves into solution.
C wrong: Both electrodes are not impure.
D wrong: One electrode must be impure copper.

12. C

A wrong: Pure copper forms at the cathode.
B wrong: Impurities come from the anode, not cathode.
C right: Copper atoms at the impure anode lose electrons to form Cu2+ ions.
D wrong: Sulfate ions are not discharged.

13. B

A wrong: The spoon must be the cathode, not anode.
B right: The object to be plated is the cathode; silver is the anode; electrolyte contains Ag+ ions.
C wrong: Sodium chloride does not supply silver ions.
D wrong: The spoon would dissolve if made the anode.

14. B

A wrong: Losing electrons would occur at the anode.
B right: Metal ions gain electrons at the negative object and form a metal coating.
C wrong: Non-metal ions are oxidised at the anode.
D wrong: The object should gain coating, not dissolve.

15. B

A wrong: Dirty object and very high current give poor/uneven coating.
B right: A clean object and low steady current give an even coating.
C wrong: Electrolyte is essential.
D wrong: Metal ions must be present in solution.

16. B

A wrong: Sodium is not produced from aqueous sodium chloride.
B right: Brine electrolysis gives hydrogen at cathode, chlorine at anode and sodium hydroxide solution remains.
C wrong: Oxygen is more likely from dilute sodium chloride, not concentrated brine.
D wrong: Sodium is not formed in aqueous electrolysis.

17. B

A wrong: Sodium is not produced in aqueous solution.
B right: In dilute sodium chloride, hydrogen forms at cathode and oxygen forms at anode.
C wrong: Sodium is not produced.
D wrong: Chlorine is favoured in concentrated chloride solution, not dilute.

18. B

A wrong: Sodium ions can move in solution.
B right: Water/H+ is reduced more easily than Na+, so hydrogen forms.
C wrong: Sodium is more reactive than hydrogen.
D wrong: Sodium ions are positive and move to the cathode.

19. A

A right: In concentrated sodium chloride, chloride ions are present in high concentration and are discharged to chlorine.
B wrong: Hydroxide ions can move to the anode.
C wrong: Oxygen can be produced from aqueous solutions.
D wrong: Chlorine forms at the anode.

20. A

A right: Ag+ ions are less reactive than hydrogen and are reduced to silver at the cathode.
B wrong: Hydrogen is not produced instead of silver here.
C wrong: Nitrate ions move to the anode, not cathode.
D wrong: OH– ions move to the anode.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

21. B

A wrong: Potassium is too reactive to be discharged from aqueous solution.
B right: Hydrogen forms at the cathode and iodide ions form iodine at the anode.
C wrong: Iodide ions are discharged rather than oxygen in this halide solution.
D wrong: Potassium is not formed.

22. B

A wrong: Potassium is not discharged from aqueous solution.
B right: Water/H+ gives hydrogen at the cathode and OH–/water gives oxygen at the anode.
C wrong: Potassium is not produced.
D wrong: Sulfate ions are not discharged to sulfur.

23. C

A wrong: Concentrated sodium chloride gives chlorine at the anode.
B wrong: Copper(II) chloride gives chlorine at the anode.
C right: Dilute sulfuric acid gives oxygen at the anode.
D wrong: Potassium bromide gives bromine at the anode.

24. C

A wrong: Sodium is not produced from aqueous sodium sulfate.
B wrong: Potassium is not produced from aqueous potassium nitrate.
C right: Copper forms at the cathode from Cu2+ ions.
D wrong: Magnesium is too reactive; hydrogen forms instead.

25. B

A wrong: Zinc is more reactive than hydrogen, so it is not usually discharged from aqueous solution at O Level.
B right: Hydrogen forms at the cathode.
C wrong: Sulfur is not a cathode product.
D wrong: Oxygen forms at the anode, not cathode.

26. A

A right: Silver ions gain electrons at the cathode to form silver.
B wrong: Nitrate ions are not normally discharged.
C wrong: Silver ions are reduced, not oxidised.
D wrong: Some metal ions, such as Ag+ and Cu2+, are discharged instead of hydrogen.

27. B

A wrong: Sodium ions are cations and go to the cathode.
B right: Bromide ions are discharged at the anode to form bromine.
C wrong: H+ moves to the cathode.
D wrong: In concentrated bromide solution, bromide is discharged rather than OH–.

28. B

A wrong: Electrons do not move through the electrolyte; ions move through the electrolyte.
B right: Electrons enter the cathode from the power supply and are used in reduction.
C wrong: Electrons do not travel through the solution freely.
D wrong: Sulfate ions carry charge through solution, not electrons.

29. B

A wrong: Positive ions gain electrons at the cathode.
B right: Negative ions lose electrons at the positive electrode, the anode.
C wrong: Positive ions do not go to the anode.
D wrong: Negative ions lose electrons, not gain them.

30. B

A wrong: Reversed.
B right: Reduction occurs at the cathode and oxidation occurs at the anode.
C wrong: Cathode is not oxidation.
D wrong: Anode is not reduction.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

31. B

A wrong: Products are reversed.
B right: Molten zinc chloride gives zinc at the cathode and chlorine at the anode.
C wrong: Hydrogen and oxygen require water.
D wrong: Molten zinc chloride conducts because ions are mobile.

32. B

A wrong: In aqueous zinc chloride, hydrogen is more likely than zinc at O Level.
B right: Hydrogen forms at the cathode and chlorine forms at the anode.
C wrong: Zinc is not normally discharged from aqueous solution here.
D wrong: Chloride ions form chlorine rather than oxygen in this chloride solution.

33. B

A wrong: Molten sodium chloride gives sodium at the cathode.
B right: Aqueous sodium chloride contains water, so hydrogen can form at the cathode.
C wrong: Molten sodium chloride gives chlorine at the anode.
D wrong: Aqueous sodium chloride conducts.

34. B

A wrong: Cryolite lowers, not increases, the melting point.
B right: Cryolite dissolves aluminium oxide and lowers the operating temperature.
C wrong: The carbon anodes react with oxygen, not cryolite as its main purpose.
D wrong: Aluminium ions already exist in molten aluminium oxide.

35. B

A wrong: Aluminium carbide formation is not the main reason.
B right: Oxygen produced at the anode reacts with graphite carbon to form carbon dioxide, so anodes wear away.
C wrong: Sodium ions are not involved.
D wrong: Graphite is consumed by reaction, not simply dissolved.

36. C

A wrong: This is the cathode reaction.
B wrong: Aluminium metal is not oxidised at the anode in extraction.
C right: Oxide ions lose electrons: 2O2– → O2 + 4e–.
D wrong: This is reduction of oxygen, not anode oxidation.

37. B

A wrong: Aluminium ions gain electrons, not lose them.
B right: Al3+ ions are reduced by gaining electrons to form aluminium.
C wrong: Aluminium ions are not gaining oxygen.
D wrong: They are not losing oxygen.

38. B

A wrong: Aluminium oxide is not rare or impossible to melt.
B right: Electrolysis needs large amounts of electricity, making extraction expensive.
C wrong: Aluminium is not extracted by carbon in a blast furnace.
D wrong: Aluminium is found mainly in compounds, not as free metal.

39. B

A wrong: Molten aluminium is product, not electrolyte.
B right: The electrolyte is molten cryolite with dissolved aluminium oxide.
C wrong: Aqueous aluminium chloride is not used.
D wrong: Solid aluminium oxide cannot conduct because ions are fixed.

40. C

A wrong: Aluminium forms at the negative electrode, not positive.
B wrong: Oxygen forms at the positive electrode.
C right: Aluminium forms at the cathode.
D wrong: Cryolite is not reduced to aluminium.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

41. B

A wrong: Sodium is not discharged from aqueous solution.
B right: Cu2+ is reduced to copper at the cathode; high Cl– concentration gives chlorine at the anode.
C wrong: Copper forms instead of hydrogen at cathode.
D wrong: Sulfate ions are not discharged to sulfur dioxide.

42. A

A right: Cu2+ ions are discharged before hydrogen ions, so copper forms first at the cathode.
B wrong: Hydrogen is less likely than copper here.
C wrong: Nitrogen dioxide is not a cathode product.
D wrong: Oxygen forms at the anode, not cathode.

43. C

A wrong: Potassium is too reactive to be discharged.
B wrong: Potassium is not formed.
C right: Hydrogen forms at the cathode and oxygen at the anode.
D wrong: Sulfate ions are not discharged to sulfur.

44. B

A wrong: This is cathode deposition.
B right: At the copper anode, copper atoms lose electrons: Cu → Cu2+ + 2e–.
C wrong: This happens at an inert anode, not copper-plating with a copper anode.
D wrong: Sulfate ions are not discharged.

45. A

A right: Cu2+ forms copper at the cathode and Cl– forms chlorine at the anode.
B wrong: Copper forms instead of hydrogen, and chlorine instead of oxygen.
C wrong: Products are reversed.
D wrong: Copper forms at the cathode, not hydrogen.

46. A

A right: Cu2+ ions are removed from solution as copper metal at the cathode, so the colour fades.
B wrong: Chloride ions are not responsible for the blue-green colour.
C wrong: With inert electrodes, copper atoms do not dissolve at the anode.
D wrong: Hydrogen ions are not the cause of the colour fading.

47. B

A wrong: Sodium ions are not discharged.
B right: Water is decomposed to hydrogen and oxygen, so the remaining sodium sulfate solution becomes more concentrated.
C wrong: Sulfate ions are not discharged.
D wrong: Gases do form.

48. B

A wrong: Cations migrate to the cathode.
B right: Anions migrate to the anode.
C wrong: Electrons do not migrate through solution.
D wrong: Neutral atoms do not migrate as charge carriers.

49. B

A wrong: Solid sodium chloride does not conduct, though solid copper does.
B right: Molten sodium chloride conducts by ions; solid copper conducts by delocalised electrons.
C wrong: Solid sugar and ethanol do not conduct.
D wrong: Solid lead(II) bromide and solid sulfur do not conduct.

50. B

A wrong: The steel object must be cathode to receive nickel.
B right: Steel object is cathode, nickel is anode, and nickel(II) sulfate supplies Ni2+ ions.
C wrong: Graphite is not the electrolyte.
D wrong: Nickel sulfate is the electrolyte, not the cathode.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.