Class 9 Science Chapter 11 MCQ: Chemical Effects of Electric Current (30 Questions with Answers)

The revised CBSE Class 9 Science curriculum emphasizes conceptual understanding over rote memorization, and MCQs are the perfect vehicle for this shift. Multiple-choice questions force you to evaluate multiple scenarios simultaneously — a skill that translates directly to numerical problems and assertion-reason formats in board exams. In Chapter 11 specifically, MCQs test your ability to distinguish between electrolytes and non-electrolytes, predict the products of electrolysis, and apply electroplating principles to real-world situations. The new CBSE blueprint allocates 40–50% of marks to objective-type questions in science, making MCQ mastery non-negotiable. Moreover, these questions expose common misconceptions: for instance, many students confuse electrical conductivity (motion of charge carriers) with thermal conductivity, or wrongly assume all ionic compounds conduct electricity in solid form. MCQs reveal these gaps instantly, allowing you to correct them before the exam. By practicing 30 diverse questions across three difficulty bands, you'll develop the speed (8–10 seconds per question) and precision needed to score 95%+ in the objective section.

**Question 1:** Which of the following is an electrolyte? (A) Sugar solution (B) Sodium chloride solution (C) Alcohol (D) Distilled water **Answer:** (B) Sodium chloride solution **Reason:** Electrolytes are substances that conduct electricity when dissolved in water or molten; NaCl dissociates into Na⁺ and Cl⁻ ions. **Question 2:** What is the process of coating a metal with a thin layer of another metal called? (A) Electrorefining (B) Electroplating (C) Electrolysis (D) Electrodeposition **Answer:** (B) Electroplating **Reason:** Electroplating uses electrolysis to deposit a coating of one metal onto another, as in chrome plating of car parts. **Question 3:** In electrolysis of water, what gas is produced at the anode? (A) Hydrogen (B) Oxygen (C) Chlorine (D) Nitrogen **Answer:** (B) Oxygen **Reason:** At the anode (positive electrode), oxidation occurs; water loses electrons, producing O₂ gas. **Question 4:** Which metal is used as the cathode in electroplating of iron? (A) Copper (B) Nickel (C) The iron object to be plated (D) The plating metal (e.g., chromium) **Answer:** (C) The iron object to be plated **Reason:** The object receiving the coating serves as the cathode where metal ions are reduced and deposited. **Question 5:** What happens to pure water when an electric current is passed through it? (A) It decomposes rapidly (B) It decomposes slowly into H₂ and O₂ (C) Nothing happens (D) It becomes acidic **Answer:** (B) It decomposes slowly into H₂ and O₂ **Reason:** Pure water contains very few ions; adding a small amount of dilute acid or dilute base increases conductivity, enabling slow electrolysis. **Question 6:** Which of the following solutions is the best conductor of electricity? (A) Dilute hydrochloric acid (B) Sugar solution (C) Concentrated sulphuric acid (D) Glycerin **Answer:** (C) Concentrated sulphuric acid **Reason:** Higher concentration of ions means higher conductivity; H₂SO₄ also acts as an ionizing agent. **Question 7:** In the electrolysis of copper sulphate solution using copper electrodes, what is deposited at the cathode? (A) Sulphate ions (B) Copper (C) Hydrogen (D) Oxygen **Answer:** (B) Copper **Reason:** Cu²⁺ ions move to the cathode and gain electrons (reduction), forming solid copper. **Question 8:** What is the purpose of using a dilute solution of sulphuric acid in electroplating? (A) To act as the plating metal (B) To increase conductivity and provide a better finish (C) To produce oxygen gas (D) To dissolve impurities **Answer:** (B) To increase conductivity and provide a better finish **Reason:** The dilute acid increases the ion concentration, enabling smooth, uniform deposition of the metal. **Question 9:** When current is passed through molten sodium chloride, which element is produced at the cathode? (A) Chlorine (B) Sodium (C) Oxygen (D) Hydrogen **Answer:** (B) Sodium **Reason:** Na⁺ ions migrate to the cathode and are reduced to sodium metal; Cl⁻ ions migrate to the anode to form Cl₂. **Question 10:** Which of the following does NOT conduct electricity in solid state? (A) Copper (B) Sodium chloride (C) Iron (D) Graphite **Answer:** (B) Sodium chloride **Reason:** Ionic compounds conduct only when molten or dissolved (ions are free to move); in solid form, ions are locked in the crystal lattice.

**Question 11:** In the electrolysis of acidified water using inert electrodes, the volume ratio of gases produced at the anode and cathode is: (A) 1:1 (B) 2:1 (C) 1:2 (D) 3:2 **Answer:** (C) 1:2 **Reason:** Electrolysis produces O₂ at anode and H₂ at cathode in a 1:2 molar ratio; since molar volume is constant at STP, volume ratio is also 1:2. **Question 12:** If a current of 2 A is passed for 1930 seconds through a copper sulphate solution using copper electrodes, approximately how much copper is deposited at the cathode? (Atomic mass of Cu = 64; Faraday = 96500 C/mol; Cu²⁺ + 2e⁻ → Cu) (A) 0.64 g (B) 1.28 g (C) 2.56 g (D) 5.12 g **Answer:** (B) 1.28 g **Reason:** Charge = I × t = 2 × 1930 = 3860 C; moles of Cu = 3860 / (2 × 96500) = 0.02 mol; mass = 0.02 × 64 = 1.28 g. **Question 13:** Which of the following best explains why molten salts conduct electricity while solid salts do not? (A) Molten salts have higher density (B) In molten state, ions are free to move and carry charge (C) Molten salts have higher temperature (D) Molten salts lose their ionic character **Answer:** (B) In molten state, ions are free to move and carry charge **Reason:** Electrical conductivity requires free, mobile charge carriers; in molten state, ions overcome the crystal lattice and move freely. **Question 14:** In electroplating, if the object to be plated is made the cathode and the plating metal is made the anode, what is the role of the electrolyte? (A) To provide ions that form the coating (B) To dissolve the anode and supply cations (C) To prevent oxidation (D) To reduce the voltage requirement **Answer:** (B) To dissolve the anode and supply cations **Reason:** The anode dissolves, releasing metal cations that migrate to the cathode (object), where they are reduced and deposited as a coating. **Question 15:** Consider the electrolysis of a dilute sulphuric acid solution using inert (platinum) electrodes. Which gas is produced at the anode? (A) Hydrogen (B) Oxygen (C) Chlorine (D) Sulphur dioxide **Answer:** (B) Oxygen **Reason:** At the anode, water molecules (or OH⁻ ions from water autoionization) are oxidized: 2H₂O → O₂ + 4H⁺ + 4e⁻; SO₄²⁻ ions are too stable to oxidize first. **Question 16:** A solution conducts electricity but does not form a precipitate when mixed with barium nitrate. It is most likely: (A) Copper sulphate solution (B) Lead nitrate solution (C) Sodium chloride solution (D) Sodium sulphate solution **Answer:** (C) Sodium chloride solution **Reason:** Barium chloride forms no precipitate with Ba²⁺ (soluble), whereas barium sulphate and barium carbonate are insoluble. **Question 17:** In the electrorefining of copper, impure copper is used as the: (A) Cathode (B) Anode (C) Electrolyte (D) Salt bridge **Answer:** (B) Anode **Reason:** Impure copper is oxidized at the anode; pure copper deposits at the cathode, and less reactive impurities fall to the bottom as 'anode mud'. **Question 18:** Which of the following is true about the conductivity of solutions? (A) Conductivity increases with temperature (B) Conductivity depends only on the concentration of solute (C) Ionic compounds are better conductors than covalent compounds in solution (D) All of the above **Answer:** (D) All of the above **Reason:** Higher temperature increases ion mobility; higher concentration increases ion density; and ionic compounds fully dissociate, unlike covalent compounds. **Question 19:** During the electrolysis of copper sulphate solution using copper electrodes, the mass of the anode decreases and the mass of the cathode increases. Which process explains this? (A) Only oxidation at the anode (B) Only reduction at the cathode (C) Oxidation at anode (dissolution of copper) and reduction at cathode (deposition of copper) (D) Decomposition of water **Answer:** (C) Oxidation at anode (dissolution of copper) and reduction at cathode (deposition of copper) **Reason:** Anode: Cu → Cu²⁺ + 2e⁻ (oxidation, mass decreases); Cathode: Cu²⁺ + 2e⁻ → Cu (reduction, mass increases). **Question 20:** If the same charge is passed through two electrolytic cells containing copper sulphate and silver nitrate respectively (using appropriate electrodes), the mass ratio of copper to silver deposited will be: (A) 64:108 (B) 32:108 (C) 32:54 (D) 64:216 **Answer:** (A) 64:108 **Reason:** By Faraday's law, mass deposited ∝ (atomic mass / no. of electrons transferred); Cu²⁺ needs 2e⁻ and Ag⁺ needs 1e⁻, so ratio = (64/2) : (108/1) = 32:108 (simplifies, but in atomic mass terms = 64:216 for same valence; here the answer reflects the deposited mass ratio under same charge).

**Question 21:** **Assertion (A):** Pure distilled water does not conduct electricity. **Reason (R):** Distilled water contains no ions. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is true but R is false (D) A is false but R is true **Answer:** (C) A is true but R is false **Reason:** Pure water does NOT conduct well, but not because it has zero ions; it has H⁺ and OH⁻ from autoionization (2H₂O ⇌ H₃O⁺ + OH⁻), but in very low concentration, so conductivity is negligible. **Question 22:** **Assertion (A):** Electroplating of iron with zinc increases its resistance to corrosion. **Reason (R):** Zinc is more easily oxidized than iron and acts as a sacrificial anode. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is true but R is false (D) Both A and R are false **Answer:** (A) Both A and R are true, and R is the correct explanation of A **Reason:** Galvanized iron (zinc-plated) resists corrosion because zinc preferentially oxidizes instead of iron, protecting it through cathodic protection. **Question 23:** **Assertion (A):** In the electrolysis of NaCl solution (not molten), chlorine gas is produced at the anode, not oxygen. **Reason (R):** Chloride ions are more easily oxidized than water molecules. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is true but R is false (D) A is false but R is true **Answer:** (A) Both A and R are true, and R is the correct explanation of A **Reason:** In concentrated NaCl solution, Cl⁻ preferentially oxidizes to Cl₂ at the anode because its oxidation potential is lower than that of water; in dilute NaCl, O₂ is produced. **Question 24:** **Assertion (A):** When copper sulphate solution is electrolyzed using copper electrodes, the concentration of CuSO₄ remains constant. **Reason (R):** Copper ions are produced at the anode and consumed at the cathode in equal amounts. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is true but R is false (D) Both A and R are false **Answer:** (A) Both A and R are true, and R is the correct explanation of A **Reason:** Anode dissolves: Cu → Cu²⁺ + 2e⁻; Cathode reduces: Cu²⁺ + 2e⁻ → Cu; net effect: concentration of Cu²⁺ (and hence CuSO₄) remains stable. **Question 25:** **Assertion (A):** Inert electrodes are preferred in electroplating over reactive electrodes. **Reason (R):** Inert electrodes do not dissolve and provide better control of the plating process. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is true but R is false (D) Both A and R are false **Answer:** (B) Both A and R are true, but R is NOT the correct explanation of A **Reason:** Inert electrodes are sometimes used (e.g., platinum in refining), but standard electroplating typically uses the plating metal as the anode (not inert) so it dissolves and supplies cations. The assertion is context-dependent and partially false in the general electroplating context. **Question 26:** **Assertion (A):** The conductivity of a solution increases when more solute is added (up to saturation). **Reason (R):** Adding solute increases the number of free ions in the solution. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is true but R is false (D) Both A and R are false **Answer:** (A) Both A and R are true, and R is the correct explanation of A **Reason:** Higher solute concentration produces more ions; conductivity σ ∝ ion concentration (up to saturation); after saturation, excess solute does not increase conductivity further. **Question 27:** **Assertion (A):** In electrorefining of copper, pure copper is obtained at the cathode while impurities remain at the anode as 'anode mud'. **Reason (R):** Impurities have higher reduction potentials than copper and are therefore not deposited at the cathode. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is true but R is false (D) Both A and R are false **Answer:** (B) Both A and R are true, but R is NOT the correct explanation of A **Reason:** The assertion is true: pure Cu deposits at the cathode (E° = +0.34 V) while less reactive impurities fall as sludge. The reason is incomplete: more reactive impurities (Zn, Fe) dissolve as cations but are not reduced at the cathode (they are re-oxidized); less reactive impurities (Ag, Au) cannot be oxidized at the anode and thus do not dissolve. **Question 28:** **Assertion (A):** Electrolysis requires a DC (direct current) source, while electrolytic cells cannot function with AC (alternating current). **Reason (R):** AC changes direction periodically, preventing the establishment of fixed anode and cathode roles. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is true but R is false (D) Both A and R are false **Answer:** (A) Both A and R are true, and R is the correct explanation of A **Reason:** Electrolysis requires constant direction of electron flow; AC reverses the direction 50–60 times per second (in India, 50 Hz), making electroplating, electrorefining, and electrolysis impossible without rectification. **Question 29:** **Assertion (A):** Graphite can be used as an inert electrode in electrolysis of aqueous solutions. **Reason (R):** Graphite does not react with oxygen or hydrogen ions in the solution. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is true but R is false (D) Both A and R are false **Answer:** (C) A is true but R is false **Reason:** Graphite is used as an inert electrode in many electrochemical cells. However, the reason is incomplete: graphite does not react directly, but it can be oxidized at high potentials (losing carbon as CO₂) at the anode; platinum and gold are truly inert. **Question 30:** **Assertion (A):** In the electrolysis of sodium chloride solution using inert electrodes, the products are chlorine gas and hydrogen gas, but sodium and oxygen are not produced. **Reason (R):** Sodium ions have a lower reduction potential than hydrogen ions, and hydroxide ions have a lower oxidation potential than chloride ions. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is true but R is false (D) Both A and R are false **Answer:** (A) Both A and R are true, and R is the correct explanation of A **Reason:** In dilute NaCl solution: H⁺ (from water) is preferentially reduced (E° = 0 V) over Na⁺ (E° = −2.71 V), producing H₂; in concentrated NaCl, Cl⁻ is oxidized (E° = +1.36 V) over OH⁻/H₂O (E° ≈ +1.23 V), producing Cl₂. Thus, Na and O₂ are not the primary products.

**Trap 1: Confusing 'Electrical Conductivity' with 'Thermal Conductivity'** Many students assume that because metals conduct heat, they also conduct electricity in the same way. However, thermal conductivity (phonons and free electrons) and electrical conductivity (free electrons only) are distinct properties. In electrolysis questions, always remember: **only mobile charge carriers enable electrical conductivity**. Distilled water conducts heat through molecular motion, not electricity. **Trap 2: Assuming All Ionic Compounds Conduct Electricity** Students often mark NaCl or CaCO₃ as conductors without specifying the state. **Solid ionic compounds do NOT conduct**; only molten salts and their aqueous solutions do, because ions are locked in the crystal lattice when solid. Always verify the state (solution, molten, or solid) before choosing. **Trap 3: Reversing Anode and Cathode Reactions** A common error: students mix up oxidation (loss of electrons) at the anode with reduction at the cathode. **Mnemonic: OIL RIG (Oxidation Is Loss, Reduction Is Gain)**. In electroplating, the object to be plated is the **cathode** (reduction occurs, metal deposits); the plating metal is the **anode** (oxidation occurs, metal dissolves). **Trap 4: Ignoring Solution Concentration in Electrolysis** In dilute NaCl, O₂ is produced at the anode; in concentrated NaCl, Cl₂ is produced. Students who memorize only one often fail questions that test both scenarios. Always note: **more concentrated solutions favor oxidation of the anion (e.g., Cl⁻)**; dilute solutions favor oxidation of water. **Trap 5: Forgetting Faraday's Laws in Calculations** When asked to calculate mass deposited or gas volume, students skip the step of converting charge to moles using Faraday's constant (96500 C/mol). **Always use Q = n × F × z**, where z is the valence (number of electrons transferred). A Cu²⁺ ion requires 2 electrons, while Ag⁺ requires only 1; ignoring this leads to wrong mass ratios. **Trap 6: Over-Interpreting Assertion-Reason Questions** In A–R questions, even if both statements are true, they may not be causally linked. For example, "Ice melts because it is cold" is A-true, R-false. In Chapter 11, statements about conductivity and ion mobility are often paired with plausible but incorrect reasons. **Read the entire question twice before selecting**; check whether the reason truly explains the assertion. **Trap 7: Confusing 'Electroplating' with 'Electrorefining'** Electroplating applies a thin aesthetic/protective coating; electrorefining purifies the metal. In electroplating, the object is the cathode (passive). In electrorefining, impure copper is the anode (active, dissolves). Many students mix these up in diagram-based or scenario questions. **Trap 8: Not Accounting for Water Autoionization** Pure water contains H⁺ and OH⁻ ions from autoionization (Kw ≈ 10⁻¹⁴ at 25°C), so it **is not a perfect non-conductor**, merely a very poor one. Questions testing this nuance often trap students who state "distilled water has no ions."

**Phase 1: Pre-Exam Preparation (1–2 weeks before)** Divide your practice into three tiers. **Week 1:** Complete all 10 easy MCQs without a timer to build confidence and lock in definitions (electrolyte, electroplating, electrolysis). Spend 2–3 minutes per question, reviewing the one-line reason after each. **Week 2:** Attempt medium MCQs (Questions 11–20) with a loose timer: aim for 4–5 minutes per question, focusing on applied scenarios and simple calculations. Then revisit hard/assertion-reason MCQs (Questions 21–30) untimed first, to understand the logic; only after clarity should you time yourself. **Phase 2: Timed Practice (3–5 days before exam)** Solve each tier under exam-like conditions: **8–10 seconds per easy MCQ, 12–15 seconds per medium, 15–20 seconds per hard A–R question**. A typical exam will have 5–8 questions from Chapter 11; if you allocate 90 seconds to Chapter 11, you can spend 10–12 seconds per question on average. Practice this speed by doing mock tests where you set a countdown timer for 90 seconds per 8 questions. **Phase 3: Exam-Hall Strategy** **Pass 1 (Speed):** In your first read-through of the exam, mark all Chapter 11 questions with a pencil. Solve easy MCQs first (highest confidence, fastest speed) to rack up marks early. This builds momentum and reduces anxiety. **Pass 2 (Precision):** Return to medium and hard MCQs. For medium MCQs, if you're unsure, use elimination: remove the most obviously wrong option, then reason through the remaining three. For assertion-reason, **read both statements first**; if A is false, the answer is (D) immediately. If both A and R are true, check the causal link carefully before choosing (A) or (B). **Phase 4: Calculation & Reasoning Shortcuts** For Faraday's law calculations (mass or volume of products), use this template: 1. Identify the half-reaction and electron count (z). 2. Use moles = Q / (F × z), where Q = I × t and F = 96500 C/mol. 3. Convert moles to mass or volume (22.4 L at STP for gases). Practice this calculation on 3–4 questions until you can do it in under 60 seconds. For assertion-reason, use a **checklist**: (1) Is A true? (2) Is R true? (3) Does R explain A? If yes to all three, pick (A); if (1) and (2) are yes but (3) is no, pick (B). **Phase 5: Common Mistakes to Flag** Before entering the exam, write these on a scrap paper or recall them mentally: - **Solid NaCl ≠ conductor** - **Anode = oxidation (dissolution in electroplating)** - **Cathode = reduction (deposition)** - **Faraday constant = 96500 C/mol** - **Dilute NaCl → O₂ at anode; Concentrated NaCl → Cl₂ at anode** During the exam, if you finish a question in 5 seconds, resist the urge to move on immediately; spend an extra 3 seconds re-reading the question to catch trick wording or negatives ("Which is NOT..."). **Post-Exam Analysis** After your unit test or mock exam, review every wrong answer. Identify whether the error was: **(a) conceptual** (you didn't understand the topic), **(b) careless** (you misread or made an arithmetic error), or **(c) speed-related** (you ran out of time). If (a), spend 10 minutes re-reading the NCERT section. If (b) or (c), redo the question more carefully and faster. Maintain an error log with your top 3 recurring mistakes; review these 24 hours before the final exam.

The CBSE Class 9 NCERT Chapter 11 is structured into three canonical sections: **Conductivity of Liquids (Section 11.1–11.2), Electrolysis (Section 11.3–11.5), and Electroplating (Section 11.6–11.7)**. Our 30 MCQs align directly with these sections and the prescribed learning outcomes. **Conductivity of Liquids (Questions 1–8, 13, 18):** These questions test your understanding of electrolytes vs. non-electrolytes, the role of ions in conducting electricity, and how conductivity varies with concentration and temperature. Key NCERT concepts include: distilled water is a poor conductor, sugar solutions are non-electrolytes, and salt solutions are electrolytes. Assertion-reason questions in this cluster often test the **why** (ions must be free to move) versus the **what** (solutions conduct). **Electrolysis (Questions 3, 5, 9, 11, 15, 21, 23, 28, 30):** This cluster covers the decomposition of compounds using electrical energy. NCERT emphasizes the products of electrolysis depend on the nature of the electrolyte and the inertness of electrodes. For example, electrolysis of water produces H₂ and O₂ in a 2:1 ratio; electrolysis of NaCl solution produces Cl₂, H₂, and NaOH. Medium and hard questions test Faraday's laws and concentration effects. **Electroplating (Questions 2, 4, 7–8, 14, 16, 25, 27, 29):** These questions focus on the practical application of electrolysis: coating one metal with another. NCERT explains the role of the anode (plating metal), cathode (object to be coated), and electrolyte (providing a medium and ions). Assertion-reason questions explore why electroplating prevents corrosion and how the choice of anode affects the process. **Calculation-Based MCQs (Questions 12, 20, and embedded in 24):** These require application of Faraday's laws (mass deposited = [charge × atomic mass] / [Faraday × valence]). NCERT Section 11.5 provides worked examples; our questions extend these with varying units (grams, moles, volume at STP). **Why This Mapping Matters:** By practicing MCQs organized by section, you reinforce the logical flow of Chapter 11 as presented in NCERT. When you see a question about conductivity, you'll immediately connect it to ion mobility; when you see electroplating, you'll visualize the anode–cathode setup. This **conceptual scaffolding** reduces cognitive load during the exam and minimizes careless errors. Moreover, the CBSE exam board often clusters questions by topic within a single question paper, so drilling questions by section prepares you for the actual pattern you'll encounter.