Introduction to the Topic

For candidates gearing up for the 71st BPSC Prelims, a firm grasp of Physics and Chemistry within the General Science syllabus is essential, as highlighted by this question from the 69th BPSC Prelims (2023) on the electrical conductivity of liquids. This topic bridges concepts of electrolytes, ions, and electrical properties, which are fundamental to understanding chemical and physical processes in everyday and industrial applications. The question’s relevance is amplified by Bihar’s focus on science education and India’s advancements in energy and material sciences. It tests candidates’ ability to identify a liquid with poor electrical conductivity among options that may seem similar, aligning with the Prelims’ objective format’s emphasis on precision.

Question and Options

Question: Which of the following liquids is a bad conductor of electricity?
(A) Salted water
(B) Orange juice
(C) Lemon juice
(D) None of the above

Analysis and Explanation

This question assesses candidates’ understanding of electrical conductivity in liquids, which depends on the presence of ions (charged particles) that can carry an electric current. Liquids that conduct electricity well are typically electrolytes, containing free ions from dissolved salts, acids, or bases. A bad conductor (or poor conductor) has few or no free ions, limiting its ability to conduct electricity. Let’s evaluate each option to determine which liquid fits this description.

• Salted water (A):
  Salted water contains sodium chloride (NaCl), which dissociates into Na⁺ and Cl⁻ ions when dissolved in water. These free ions enable salted water to conduct electricity effectively, making it a strong electrolyte. For example, seawater or saline solutions are good conductors due to high ion concentrations.
  Evaluation: Incorrect, as salted water is a good conductor of electricity due to its abundant ions.
• Orange juice (B):
  Orange juice contains natural sugars, water, and small amounts of organic acids (e.g., citric acid), vitamins, and trace minerals. While citric acid can partially dissociate to produce H⁺ ions and citrate ions, the concentration of free ions in orange juice is relatively low compared to strong electrolytes like salted water. Additionally, the high sugar content (non-ionic) and lower ionizable components make orange juice a poor conductor of electricity. It conducts slightly better than pure water (a very poor conductor) but significantly less than solutions with strong electrolytes.
  Evaluation: Correct, as orange juice is a bad conductor due to its low concentration of free ions.
• Lemon juice (C):
  Lemon juice is rich in citric acid, a weak organic acid that partially dissociates in water to produce H⁺ ions and citrate ions. This dissociation results in a higher concentration of free ions compared to orange juice, as lemon juice is more acidic (lower pH, typically around 2–3). The presence of these ions allows lemon juice to conduct electricity better than orange juice, though not as effectively as salted water. Lemon juice is considered a moderate conductor due to its ionic content.
  Evaluation: Incorrect, as lemon juice is a moderate conductor of electricity due to its acidic nature and ion production.
• None of the above (D):
  This option would be correct if all listed liquids were good conductors of electricity. However, orange juice (B) is a bad conductor due to its low ion content, while salted water and lemon juice conduct electricity to varying degrees. Therefore, this option does not apply, as option B fits the question’s criteria.
  Evaluation: Incorrect, as orange juice is a bad conductor, negating this choice.

Key Insights:

• Electrical conductivity in liquids depends on the presence and mobility of free ions, with strong electrolytes (e.g., NaCl solutions) conducting best.
• Weak electrolytes (e.g., citric acid in lemon juice) conduct moderately, while liquids with low ion content (e.g., orange juice) are poor conductors.
• Pure water is a very poor conductor due to minimal ion presence, but most natural liquids contain some ions, affecting their conductivity.
• Distractors test candidates’ ability to differentiate between strong, moderate, and weak conductors based on chemical composition.
• The question’s moderate difficulty lies in distinguishing subtle differences in ion content among seemingly similar liquids.

Correct Answer

Correct Answer: (B) Orange juice
Reason: Orange juice is a bad conductor of electricity due to its low concentration of free ions, primarily from weak organic acids like citric acid, diluted by sugars and water. Salted water (A) is a strong conductor due to Na⁺ and Cl⁻ ions, lemon juice (C) is a moderate conductor due to higher citric acid content, and option D is incorrect as orange juice fits the criteria.

Five Probable Questions of Similar Difficulty

To enhance preparation for the 71st BPSC Prelims, here are five chemistry and physics-related questions of comparable difficulty, focusing on electrical conductivity and electrolytes, with concise explanations:

1. Question: Which of the following is a strong electrolyte in aqueous solution?
   • (A) Sugar syrup
   • (B) Sodium chloride
   • (C) Acetic acid
   • (D) Ethanol
     Answer: (B) Sodium chloride
     Explanation: NaCl fully dissociates into ions, making it a strong electrolyte, unlike sugar, acetic acid (weak), or ethanol (non-electrolyte).
2. Question: Why does pure water conduct electricity poorly?
   • (A) High ion concentration
   • (B) Low ion concentration
   • (C) High viscosity
   • (D) Low density
     Answer: (B) Low ion concentration
     Explanation: Pure water has minimal H⁺ and OH⁻ ions, limiting conductivity, unlike ion-rich solutions.
3. Question: Which liquid is likely to conduct electricity better than lemon juice?
   • (A) Distilled water
   • (B) Saltwater
   • (C) Apple juice
   • (D) Sugar solution
     Answer: (B) Saltwater
     Explanation: Saltwater’s high Na⁺ and Cl⁻ ion content surpasses lemon juice’s moderate ion concentration from citric acid.
4. Question: What type of substance is a non-conductor in aqueous solution?
   • (A) Strong acid
   • (B) Ionic salt
   • (C) Sugar
   • (D) Weak base
     Answer: (C) Sugar
     Explanation: Sugar (non-ionic) does not produce ions in solution, unlike acids, salts, or bases.
5. Question: Which factor most affects a liquid’s electrical conductivity?
   • (A) Temperature only
   • (B) Presence of free ions
   • (C) Color of the liquid
   • (D) Volume of the liquid
     Answer: (B) Presence of free ions
     Explanation: Free ions enable current flow, while temperature may enhance conductivity but is secondary to ion presence.

Key Terms Explained

• Electrical Conductivity: Ability of a liquid to conduct electric current, dependent on free ions.
• Electrolyte: Substance that produces ions in solution, enabling conductivity (e.g., NaCl, citric acid).
• Salted Water: Strong electrolyte with Na⁺ and Cl⁻ ions, highly conductive.
• Orange Juice: Weak conductor due to low ion content from citric acid and high non-ionic sugars.
• Lemon Juice: Moderate conductor due to citric acid’s partial dissociation into H⁺ and citrate ions.
• Ions: Charged particles (e.g., Na⁺, H⁺) that carry electric current in solutions.
• Citric Acid: Weak organic acid in citrus juices, contributing limited ions for conductivity.
• Non-Electrolyte: Substance (e.g., sugar) that does not produce ions, resulting in poor conductivity.

Preparation Strategies for 71st BPSC Prelims

To excel in physics and chemistry questions like this for the 71st BPSC Prelims, adopt these strategies:

• Study Electrolytes: Understand the role of ions in conductivity, distinguishing strong, weak, and non-electrolytes.
• Compare Liquids: Memorize conductivity properties of common liquids (e.g., saltwater vs. fruit juices) based on ion content.
• Practice Conceptual Questions: Solve problems on conductivity and electrolyte behavior to sharpen analytical skills.
• Link to Applications: Relate conductivity to real-world uses like electroplating or battery technology, relevant to Bihar’s industrial context.
• Master Mock Tests: Practice objective questions under timed conditions to improve accuracy and manage negative marking (1/3rd per wrong answer).

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• Website: Download mock tests, previous year papers (e.g., 69th BPSC Prelims), and structured study materials.

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• Expert Support: Attend doubt-clearing sessions to clarify concepts like conductivity and electrolyte properties.

By leveraging Crack Target’s resources, aspirants can confidently tackle science-related questions, securing a competitive edge in the 71st BPSC Prelims. For additional 69th BPSC questions or specific topics, please share, and I’ll provide a professional response with a distinct, engaging style, maintaining professional language as requested.