Q30. Which of the following has the highest value of resistivity?
[SSC CGL 2023 Tier I, 17 July, Shift 1]
A. Silver
B. Nichrome
C. Chromium
D. Iron
Answer: B. Nichrome
Explanation: Nichrome is a nickel–chromium alloy with far greater resistivity than the listed pure metals. Its high resistance and oxidation tolerance make it suitable for heating elements. Silver, by contrast, has extremely low resistivity and is one of the best electrical conductors.
Q29. Which of the following material is a conductor of electricity?
[SSC MTS 2022 cycle, held 8 May 2023, Shift 2]
A. Glass
B. Mica
C. Silver
D. Ebonite
Answer: C. Silver
Explanation: Silver is a metal with abundant mobile charge carriers and exceptionally high electrical conductivity. Glass, mica and ebonite are normally electrical insulators. Although silver conducts better than copper, its cost limits extensive use in ordinary household wiring.
Q28. Which of the following is a good conductor of heat but a bad conductor of electricity?
[RSMSSB Forest Guard, 13 November 2022, Shift 2]
A. Copper
B. Mica
C. Gold
D. Ebonite
Answer: B. Mica
Explanation: Mica is an effective electrical insulator and can transmit heat while withstanding elevated temperatures. Its combination of heat tolerance and dielectric strength is valuable in electrical equipment. Relative to metals, however, its thermal conductivity is modest; the comparison is among these options.
Q27. Which of the following elements has the highest conductivity at 298.15 K?
[Delhi Police Head Constable AWO/TPO, 28 October 2022, Shift 1]
A. Gold
B. Iron
C. Copper
D. Sodium
Answer: C. Copper
Explanation: At approximately room temperature, copper conducts electricity better than gold, iron and sodium. Its low electrical resistivity and practical availability make it highly useful in cables and electrical apparatus. Silver would rank above copper, but silver is not one of the choices.
Q26. Arrange the following materials in ascending order of electrical conductivity at 298.15 K: (a) Copper, (b) Sodium, (c) Iron, (d) Gold.
[Delhi Police Head Constable AWO/TPO, 28 October 2022, Shift 3]
A. (c), (b), (d), (a)
B. (a), (b), (d), (c)
C. (d), (a), (c), (b)
D. (b), (c), (a), (d)
Answer: A. (c), (b), (d), (a)
Explanation: Electrical conductivity generally varies with electron mobility and scattering in the material. Among these four elements near room temperature, iron has the lowest conductivity, followed by sodium, then gold, while copper conducts best. Therefore the increasing sequence is c–b–d–a.
Q25. Which of the following properties is required for a material to be used in the filament of an electric bulb?
[RRB Group D, 11 October 2022, Shift 2]
A. Low temperature
B. Low melting point
C. High resistivity
D. High conductivity
Answer: C. High resistivity
Explanation: An incandescent bulb filament needs sufficient electrical resistance to become very hot when current passes through it. It also needs an exceptionally high melting point to survive incandescent temperatures. Tungsten satisfies these requirements; a highly conducting, low-resistance filament would be less suitable.
Q24. Which of the following represents materials in increasing order of their electrical resistance?
[RRB Group D, 6 October 2022, Shift 3]
A. Insulators, conductors, alloys
B. Insulators, alloys, conductors
C. Conductors, alloys, insulators
D. Alloys, conductors, insulators
Answer: C. Conductors, alloys, insulators
Explanation: For comparable dimensions, good conductors offer the least resistance to charge flow. Many alloys resist electron movement more than pure conducting metals. Insulators offer the greatest resistance because they have very few freely moving charges. Hence the listed progression is conductors, alloys, insulators.
Q23. Copper is used in _______ due to its low resistivity.
[RRB Group D, 27 September 2022, Shift 2]
A. Toasters
B. Heaters
C. Transmission lines
D. Electric bulbs
Answer: C. Transmission lines
Explanation: Copper has low electrical resistivity, which reduces energy loss as current flows through a conductor. Therefore it is suited to power-carrying cables and transmission conductors. Toasters and heaters deliberately employ comparatively high-resistance alloys to generate useful heat.
Q22. Which of the following statements about electrical conductivity in ionic compounds is correct?
[RRB Group D, 19 September 2022, Shift 1]
A. Ionic compounds conduct poorly in both solid and molten states.
B. Ionic compounds conduct in the solid state but not when molten.
C. Ionic compounds conduct when molten but not in the solid state.
D. Ionic compounds conduct in both solid and molten states.
Answer: C. Ionic compounds conduct when molten but not in the solid state.
Explanation: In a solid ionic crystal, positive and negative ions occupy fixed lattice positions and cannot move freely. Melting breaks the rigid arrangement and allows mobile ions to carry electric charge. Thus ionic compounds ordinarily conduct electricity when molten, but not as solids.
Q21. Consider the statements:
I. Graphite is a bad conductor of electricity.
II. Each carbon atom in graphite bonds to three other carbon atoms in a hexagonal plane.
Which is correct?
[RRB Group D, 25 August 2022, Shift 3]
A. Both statements are correct.
B. Both statements are incorrect.
C. I is correct and II is incorrect.
D. II is correct and I is incorrect.
Answer: D. II is correct and I is incorrect.
Explanation: Statement I is false because delocalized electrons make graphite conductive. Statement II is true: graphite has layered hexagonal sheets in which carbon atoms form three covalent bonds each. This bonding arrangement leaves electrons available for movement through the structure.
