chemical effects of electric current set- B

 

Set 2: Chemical Effects of Electric Current — Advanced Application-Based MCQs

Introduction

This set contains 50 multiple-choice questions (MCQs) focusing on application-based and analytical aspects of the Chemical Effects of Electric Current chapter for Class 8 (NCERT/JKBOSE/CBSE). The questions explore real-life scenarios, experimental setups, and conceptual depth, including electroplating principles, electrolysis of water, conductivity testing, and the role of electrodes. Each question is unique and non-repetitive across the set.

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📌 Quiz: Science

📚 Subject: SCIENCE

🏫 Class: CLASS 8

📖 Chapter: Chemical Effects Of electric Current-B

📝 Questions: 50

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SCIENCE | Chemical Effects Of electric Current-B

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Q1. Why does distilled water not conduct electricity, but tap water does?

A. Distilled water has more hydrogen

B. Tap water has dissolved salts that provide ions

C. Distilled water is heavier

D. Tap water has more oxygen

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Q2. In an LED, what happens if the longer lead is connected to the negative terminal and the shorter lead to the positive terminal?

A. LED glows brighter

B. LED does not glow

C. LED gets damaged permanently

D. LED glows but with different colour

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Q3. During electroplating of copper on an iron key, the iron key is made the cathode. Why?

A. To attract positive copper ions from the solution

B. To repel copper ions

C. To dissolve the key

D. To make the key an anode

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Q4. Which of the following statements about electrodes is correct?

A. Anode is always negative

B. Cathode is always positive

C. Anode attracts positive ions

D. Cathode attracts positive ions

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Q5. Why is a small amount of acid or base added to water during electrolysis of water?

A. To increase the volume of water

B. To make water a better conductor by providing ions

C. To change the colour of water

D. To cool the water

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Q6. In electroplating, the thickness of the plated layer depends on:

A. Colour of the electrolyte

B. Duration of current flow and strength of current

C. Size of the container

D. Type of beaker used

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Q7. An object is electroplated with silver. What is the likely composition of the electrolyte?

A. Silver nitrate solution

B. Copper sulphate solution

C. Sodium chloride solution

D. Zinc sulphate solution

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Q8. Why does an LED glow even with a weak current, but a bulb does not?

A. LED works on heating effect

B. Bulb requires high temperature to heat the filament, LED works on electroluminescence

C. LED has no resistance

D. Bulb uses AC current only

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Q9. Which of the following is NOT a chemical effect of electric current?

A. Formation of gas bubbles at electrodes

B. Deposition of metal on cathode

C. Change in colour of the solution

D. Heating of the wire

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Q10. In the electroplating of an iron spoon with copper, the anode is made of copper. What happens to the copper anode over time?

A. It gains mass

B. It loses mass (dissolves)

C. It remains unchanged

D. It turns into iron

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Q11. Why is a layer of zinc electroplated on iron objects like bridges and railings?

A. Zinc is cheaper than iron

B. Zinc is harder than iron

C. Zinc prevents rusting by corroding itself instead of iron

D. Zinc makes iron magnetic

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Q12. What is the role of the electrolyte in electroplating?

A. To provide a path for electrons only

B. To provide ions of the metal to be plated and complete the circuit

C. To dissolve the object

D. To act as an insulator

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Q13. If you use a copper anode and an iron cathode in copper sulphate solution, what colour change do you observe in the solution after some time?

A. Colour changes from blue to green

B. Colour remains blue (if anode dissolves at same rate as deposition)

C. Colour changes to colourless

D. Colour changes to red

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Q14. Which of the following liquids is a poor conductor but can become a good conductor if a little salt is added?

A. Vegetable oil

B. Distilled water

C. Petrol

D. Kerosene

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Q15. Why is a resistance (resistor) often used in series with an LED in a circuit?

A. To increase the brightness

B. To limit current and prevent damage to the LED

C. To change the colour of LED

D. To make LED work on AC

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Q16. In the electrolysis of water with a few drops of sulphuric acid, which gas is collected at the cathode?

A. Oxygen

B. Hydrogen

C. Chlorine

D. Nitrogen

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Q17. Which of the following is an example of an object that is electroplated not for decoration but for a functional purpose?

A. Gold-plated watch

B. Silver-plated spoon

C. Tin-plated food cans

D. Chrome-plated car logo

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Q18. A student tests a liquid with an LED conductivity tester. The LED glows dimly. What can be concluded?

A. The liquid is a perfect conductor

B. The liquid is a poor conductor but not an insulator

C. The liquid is distilled water

D. The circuit is broken

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Q19. Why can't we electroplate a plastic toy directly?

A. Plastic is too expensive

B. Plastic is a non-conductor, so no current flows

C. Plastic melts in the electrolyte

D. Plastic reacts with the electrolyte

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Q20. In electroplating, if the object to be plated is made the anode instead of the cathode, what will happen?

A. The object will get plated normally

B. The object will dissolve into the solution

C. The electrolyte will solidify

D. Nothing will happen

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Q21. Which of the following is a good conductor of electricity in liquid state but a poor conductor in solid state?

A. Copper metal

B. Sodium chloride (salt)

C. Iron metal

D. Graphite

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Q22. What is the purpose of using an LED instead of a bulb in a tester for liquids?

A. LED is cheaper and longer lasting

B. LED can detect very weak currents that a bulb cannot

C. LED works without a battery

D. LED changes colour for different liquids

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Q23. During electroplating with copper, if the copper sulphate solution is not stirred, what might happen?

A. The plating will be uniform

B. The solution near the cathode becomes depleted of Cu²⁺ ions, causing poor plating

C. The anode will stop dissolving

D. The solution will turn green

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Q24. Which of the following statements about electrodes is INCORRECT?

A. Electrodes are usually made of metals or graphite

B. Electrodes can be inert (like platinum) or active (like copper)

C. Inert electrodes do not participate in the chemical reaction

D. Graphite cannot be used as an electrode because it is a non-metal

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Q25. An iron nail is electroplated with nickel. The electrolyte is nickel sulphate solution. The anode should be made of:

A. Iron

B. Nickel

C. Copper

D. Carbon

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Q26. Why do we add a few drops of dilute sulphuric acid to water before performing electrolysis of water?

A. To produce more oxygen

B. To increase the conductivity of water

C. To produce hydrogen only

D. To cool the water

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Q27. What is the advantage of electroplating with chromium over zinc?

A. Chromium is cheaper

B. Chromium is harder and gives a shiny, scratch-resistant finish

C. Chromium does not conduct electricity

D. Chromium is more reactive

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Q28. In a circuit testing conductivity, the LED glows brightly for liquid A, dimly for liquid B, and not at all for liquid C. Which statement is correct?

A. A is distilled water, B is salt water, C is vinegar

B. A is salt water, B is tap water, C is distilled water

C. A is vinegar, B is salt water, C is tap water

D. A is distilled water, B is tap water, C is salt water

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Q29. Which of the following is NOT a reason for electroplating?

A. To make metals more reactive

B. To prevent corrosion

C. To improve appearance

D. To make the object more durable

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Q30. During the electrolysis of copper sulphate solution using copper electrodes, the colour of the solution remains blue. Why?

A. No reaction occurs

B. Copper dissolves at the anode and deposits at the cathode at the same rate

C. The solution turns colourless but appears blue

D. Copper sulphate is not used

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Q31. An LED has a forward voltage of 2V and requires 10 mA current. If connected to a 6V battery without a resistor, what will happen?

A. LED glows normally

B. LED glows dimly

C. LED will be damaged due to excess current

D. LED does not glow

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Q32. Which of the following is an example of electroplating for economic reasons?

A. Gold plating on expensive jewellery

B. Silver plating on copper wires to improve conductivity

C. Chromium plating on plastic

D. Tin plating on iron to use cheaper iron instead of stainless steel

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Q33. In an electroplating experiment, the mass of the cathode increased by 0.5 g. The mass of the anode:

A. Increased by 0.5 g

B. Decreased by 0.5 g

C. Remained same

D. Decreased by 1.0 g

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Q34. Why is carbon (graphite) used as an electrode in some electrolysis experiments?

A. It is shiny and decorative

B. It is inert (does not react with many electrolytes) and conducts electricity

C. It is cheaper than metals

D. It melts easily

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Q35. Which liquid among the following will show the highest deflection in a galvanometer when used in a conductivity test?

A. 1% sugar solution

B. 1% salt solution

C. 1% vinegar

D. 1% alcohol solution

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Q36. A student electroplates a copper key with silver. The electrolyte is silver nitrate. After some time, the solution becomes blue. What is the most likely reason?

A. Silver nitrate turned blue by itself

B. Copper from the key dissolved into the solution as Cu²⁺ ions

C. The beaker was dirty

D. The battery was reversed

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Q37. Why is it important that the object to be electroplated is thoroughly cleaned before the process?

A. To make it heavier

B. To remove grease and oxides so that the metal layer adheres properly

C. To increase the current flow

D. To dissolve the object faster

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Q38. In the electrolysis of acidified water, the volume of hydrogen collected at the cathode is double that of oxygen at the anode. Why?

A. Hydrogen is lighter

B. Water molecule (H₂O) has two hydrogen atoms and one oxygen atom

C. Hydrogen escapes faster

D. Oxygen dissolves in water

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Q39. Which of the following is NOT an electroplated object?

A. Iron nails coated with zinc (galvanised nails)

B. Steel bicycle rim coated with chromium

C. Aluminium foil

D. Tin-coated steel food cans

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Q40. What happens to the pH of copper sulphate solution during electroplating with copper electrodes?

A. pH increases

B. pH decreases

C. pH remains nearly constant

D. pH becomes zero

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Q41. Why is it dangerous to touch an electrical switch with wet hands?

A. Wet hands increase body resistance

B. Wet hands (containing sweat/salts) conduct electricity, increasing shock risk

C. Water damages the switch

D. Wet hands make the switch slippery

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Q42. In a conductivity tester using an LED, if the LED does not glow even when the liquid is a good conductor, what could be the possible fault?

A. The liquid is too hot

B. The leads of the LED are reversed

C. The liquid is too cold

D. The beaker is too small

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Q43. Which metal is commonly electroplated on iron objects used in marine environments (ships) to prevent rusting?

A. Gold

B. Silver

C. Zinc (sacrificial anodes)

D. Tin

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Q44. During electroplating, if the current is too high, what defect may occur?

A. The plating will be too thin

B. The plating will be rough, dark, or powdery

C. The object will dissolve

D. The electrolyte will freeze

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Q45. Which of the following statements is true about distilled water and rainwater?

A. Both are equally good conductors

B. Distilled water is a better conductor than rainwater

C. Rainwater is a better conductor because it dissolves CO₂ and other gases forming ions

D. Neither conducts electricity

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Q46. In the electroplating of a silver spoon with gold, the electrolyte should be:

A. Silver nitrate solution

B. Gold chloride or gold cyanide solution

C. Copper sulphate solution

D. Sodium chloride solution

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Q47. Why are cyanide-based electrolytes used in gold and silver electroplating even though they are toxic?

A. They are cheaper

B. They produce smoother, brighter, and more adherent deposits

C. They work at higher temperatures

D. They are non-toxic

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Q48. A student sets up an electroplating experiment but forgets to add any electrolyte; only distilled water is used. What will happen?

A. The object will be plated very quickly

B. No plating occurs because distilled water does not conduct electricity

C. The anode will dissolve rapidly

D. The object will get a thick coating

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Q49. In the chemical effect of electric current, the amount of metal deposited on the cathode depends on:

A. Only the voltage

B. Only the time

C. The product of current and time (charge passed)

D. Only the type of metal

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Q50. Why is a layer of silver electroplated on copper wires used in some high-frequency electronic applications?

A. To make them heavier

B. Silver has lower resistivity than copper, improving conductivity at high frequencies

C. To make them look beautiful

D. To make them magnetic

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