Redox Reactions Practice

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NEET Chemistry - Chapter 6

Redox Reactions Practice Tests

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Oxidation concept
1. Oxidation is best defined as:
- A. Loss of electrons (Correct)
- B. Gain of electrons
- C. Gain of neutrons
- D. Loss of mass
Explanation: Loss of electrons is the modern definition of oxidation.
Reduction concept
2. Reduction is best defined as:
- A. Gain of electrons (Correct)
- B. Loss of electrons
- C. Gain of oxygen
- D. Loss of hydrogen
Explanation: Gain of electrons is the modern definition of reduction.
Oxidation number
3. Oxidation number of fluorine in compounds is almost always:
- A. -1 (Correct)
- B. +1
- C. 0
- D. +2
Explanation: Fluorine is the most electronegative element.
Oxidation number
4. Oxidation number of oxygen in most compounds is:
- A. -2 (Correct)
- B. -1
- C. 0
- D. +2
Explanation: Exceptions include peroxides, superoxides, and OF2.
Oxidation number
5. Oxidation number of sulfur in $SO_2$ is:
- A. +4 (Correct)
- B. +6
- C. +2
- D. 0
Explanation: Let sulfur be x: x + 2(-2) = 0, so x = +4.
Oxidation number
6. Oxidation number of nitrogen in $HNO_3$ is:
- A. +5 (Correct)
- B. +3
- C. +1
- D. -3
Explanation: 1 + x + 3(-2) = 0 gives x = +5.
Oxidation number
7. Oxidation number of chlorine in $KClO_3$ is:
- A. +5 (Correct)
- B. +3
- C. +1
- D. +7
Explanation: 1 + x + 3(-2) = 0, so chlorine is +5.
Oxidation number
8. Oxidation number of carbon in methane is:
- A. -4 (Correct)
- B. +4
- C. 0
- D. -2
Explanation: Hydrogen is +1, so carbon becomes -4.
Agent idea
9. The species that causes oxidation of another species is:
- A. Oxidising agent (Correct)
- B. Reducing agent
- C. Catalyst
- D. Indicator
Explanation: It accepts electrons and itself gets reduced.
Agent idea
10. The species that causes reduction of another species is:
- A. Reducing agent (Correct)
- B. Oxidising agent
- C. Solvent
- D. Electrolyte
Explanation: It donates electrons and itself gets oxidised.
Electron transfer
11. In a redox reaction, the number of electrons lost is always equal to:
- A. Number of electrons gained (Correct)
- B. Oxidation number of oxygen
- C. Total charge of products
- D. Number of atoms
Explanation: Charge balance demands equality.
Disproportionation
12. A reaction where the same species is both oxidised and reduced is called:
- A. Disproportionation (Correct)
- B. Neutralisation
- C. Hydrolysis
- D. Condensation
Explanation: One oxidation state splits into higher and lower states.
Comproportionation
13. When two oxidation states of the same element combine to form an intermediate state, the process is:
- A. Comproportionation (Correct)
- B. Disproportionation
- C. Polymerisation
- D. Sublimation
Explanation: It is the reverse tendency of disproportionation.
Oxygen-hydrogen view
14. Addition of hydrogen to a substance is generally:
- A. Reduction (Correct)
- B. Oxidation
- C. Neutralisation
- D. Hydration
Explanation: Gain of hydrogen corresponds to reduction in older definitions.
Oxygen-hydrogen view
15. Addition of oxygen to a substance is generally:
- A. Oxidation (Correct)
- B. Reduction
- C. Ionisation
- D. Hydrolysis
Explanation: Gain of oxygen raises oxidation state in many common reactions.
Oxidation number
16. Oxidation number of Mn in $MnO_2$ is:
- A. +4 (Correct)
- B. +2
- C. +7
- D. +6
Explanation: x + 2(-2) = 0 gives x = +4.
Oxidation number
17. Oxidation number of phosphorus in $H_3PO_4$ is:
- A. +5 (Correct)
- B. +3
- C. 0
- D. +1
Explanation: 3(+1) + x + 4(-2) = 0 gives x = +5.
Oxidation number
18. Oxidation number of chromium in $Cr_2O_7^{2-}$ is:
- A. +6 (Correct)
- B. +3
- C. +7
- D. +4
Explanation: 2x + 7(-2) = -2 gives x = +6.
Reaction spotting
19. Which process is an oxidation?
- A. $Fe^{2+} \to Fe^{3+}$ (Correct)
- B. $Cl_2 \to 2Cl^-$
- C. $Cu^{2+} \to Cu$
- D. $Ag^+ \to Ag$
Explanation: Oxidation state rises from +2 to +3.
Reaction spotting
20. Which process is a reduction?
- A. $Cu^{2+} \to Cu$ (Correct)
- B. $Fe^{2+} \to Fe^{3+}$
- C. $H_2 \to 2H^+$
- D. $2I^- \to I_2$
Explanation: Oxidation state decreases from +2 to 0.
NEET trap
21. In a redox equation, a spectator ion is one that:
- A. Does not change oxidation state (Correct)
- B. Always forms precipitate
- C. Always balances charge alone
- D. Acts only as catalyst
Explanation: It remains unchanged overall.
NEET trap
22. The best first step in oxidation-number method is to:
- A. Assign oxidation numbers to changing atoms (Correct)
- B. Write molarity relation
- C. Find molecular mass
- D. Count valence electrons
Explanation: This reveals the oxidation and reduction changes immediately.
Concept summary
23. Redox reactions are fundamentally reactions involving:
- A. Electron transfer (Correct)
- B. Only proton transfer
- C. Only heat transfer
- D. Only bond cleavage
Explanation: Electron movement is the core idea.
Concept summary
24. If oxidation number of an element decreases, the species is:
- A. Reduced (Correct)
- B. Oxidised
- C. Hydrolysed
- D. Neutralised
Explanation: Decrease in oxidation state means gain of electrons.
Concept summary
25. The strongest quick test for redox is to check whether:
- A. Any oxidation number changes (Correct)
- B. Temperature changes
- C. A gas is evolved
- D. Water is formed
Explanation: Redox is identified by oxidation-state change.
Balancing basics
26. In oxidation-number balancing, total increase in oxidation number equals:
- A. Total decrease in oxidation number (Correct)
- B. Total number of atoms
- C. Charge of solvent
- D. Sum of coefficients
Explanation: Electron loss equals electron gain.
Acidic medium
27. In acidic medium, oxygen deficiency is balanced by adding:
- A. $H_2O$ (Correct)
- B. $OH^-$
- C. $O_2$
- D. $H_2$
Explanation: Water supplies oxygen during balancing in acidic medium.
Acidic medium
28. In acidic medium, hydrogen deficiency is balanced by adding:
- A. $H^+$ (Correct)
- B. $OH^-$
- C. $H_2$
- D. $H_2O_2$
Explanation: Hydrogen ions are used in acidic solution balancing.
Basic medium
29. In basic medium, excess $H^+$ is neutralised by adding:
- A. $OH^-$ (Correct)
- B. $H_2O$
- C. $O_2$
- D. $Na^+$
Explanation: Hydroxide cancels hydrogen ions to form water.
Half-reaction
30. The ion-electron method is especially convenient for:
- A. Balancing ionic redox equations (Correct)
- B. Finding bond order
- C. Naming compounds
- D. Finding lattice enthalpy
Explanation: It isolates oxidation and reduction halves cleanly.
Half-reaction
31. A half-reaction shows:
- A. Only oxidation or only reduction separately (Correct)
- B. The full mechanism always
- C. Only spectator ions
- D. Only products
Explanation: Separate halves are balanced before recombining.
Acidic product
32. In acidic medium, permanganate ion is usually reduced to:
- A. $Mn^{2+}$ (Correct)
- B. $MnO_2$
- C. $Mn$
- D. $MnO_4^{2-}$
Explanation: That is the standard acidic-medium product.
Neutral/basic product
33. In neutral or basic medium, permanganate ion commonly gives:
- A. $MnO_2$ (Correct)
- B. $Mn^{2+}$
- C. $Mn$
- D. $Mn^{7+}$
Explanation: Permanganate is reduced to manganese dioxide outside acidic medium.
Dichromate
34. In acidic medium, dichromate ion is reduced to:
- A. $Cr^{3+}$ (Correct)
- B. $CrO_4^{2-}$
- C. Cr metal
- D. $Cr^{6+}$
Explanation: Chromium changes from +6 to +3.
n-factor
35. n-factor of $KMnO_4$ in acidic medium is:
- A. 5 (Correct)
- B. 3
- C. 1
- D. 2
Explanation: Mn changes from +7 to +2, a 5-electron change.
n-factor
36. n-factor of $KMnO_4$ in neutral/basic medium is:
- A. 3 (Correct)
- B. 5
- C. 2
- D. 1
Explanation: Mn changes from +7 to +4 in MnO2.
n-factor
37. n-factor of $K_2Cr_2O_7$ in acidic medium is:
- A. 6 (Correct)
- B. 3
- C. 2
- D. 1
Explanation: Two Cr atoms each drop from +6 to +3.
Equivalent mass
38. Equivalent mass of an oxidising agent is:
- A. Molar mass divided by n-factor (Correct)
- B. Molar mass times n-factor
- C. Atomic mass divided by valency only
- D. Always equal to molar mass
Explanation: Equivalent mass uses the electron-change count.
Equivalent mass
39. Equivalent mass of $KMnO_4$ in acidic medium is $\dfrac{158}{5}$ because:
- A. Its n-factor is 5 (Correct)
- B. Its molarity is 5
- C. It has 5 oxygen atoms
- D. It gives 5 products
Explanation: Equivalent mass is molar mass divided by n-factor.
Equivalent mass
40. Equivalent mass of $K_2Cr_2O_7$ in acidic medium is:
- A. 49 (Correct)
- B. 98
- C. 294
- D. 147
Explanation: Molar mass 294 divided by n-factor 6 gives 49.
Oxalate
41. n-factor of oxalate ion in acidic medium is:
- A. 2 (Correct)
- B. 1
- C. 4
- D. 5
Explanation: Each oxalate loses 2 electrons overall on oxidation to CO2.
Iodide
42. In $2I^- \to I_2 + 2e^-$, n-factor of iodide is:
- A. 1 (Correct)
- B. 2
- C. 0.5
- D. 3
Explanation: Each iodide loses one electron.
Balancing check
43. A correctly balanced redox equation must conserve:
- A. Mass and charge (Correct)
- B. Mass only
- C. Charge only
- D. Volume only
Explanation: Both atoms and net charge must balance.
Method choice
44. For ionic equations in solution, the most systematic redox balancing method is:
- A. Ion-electron method (Correct)
- B. Trial and error only
- C. Molecular mass method
- D. Lewis structure method
Explanation: It is neat and reliable in aqueous medium.
Method choice
45. For simpler molecular redox equations, the oxidation-number method is popular because it is:
- A. Quick and direct (Correct)
- B. Only graph-based
- C. Independent of charge
- D. Used only for organics
Explanation: It focuses on atoms whose oxidation states change.
Acidic steps
46. In acidic-medium balancing, after balancing atoms except O and H, the next correct order is usually:
- A. Balance O with $H_2O$, H with $H^+$, then charge with electrons (Correct)
- B. Balance H with $OH^-$, then O with $O_2$
- C. Add electrons before atoms
- D. Add catalyst and then water
Explanation: That is the standard sequence.
Basic steps
47. In basic-medium balancing, after obtaining the acidic form of the equation, you generally:
- A. Add $OH^-$ to both sides to neutralise $H^+$ (Correct)
- B. Multiply all coefficients by 2
- C. Remove all water molecules
- D. Set charge to zero directly
Explanation: This converts the acidic-balance form into basic-medium form.
Numerical logic
48. The total equivalents of oxidant consumed must equal the total equivalents of reductant because:
- A. Electron transfer must balance (Correct)
- B. Masses must be equal
- C. Volumes must match
- D. Pressures must match
Explanation: Equivalent concept encodes electron balance.
NEET trap
49. A common balancing mistake is forgetting to remove water molecules that appear:
- A. On both sides after simplification (Correct)
- B. Only on product side
- C. Only in acidic medium
- D. Only in basic medium
Explanation: Final balanced equations should be simplified.
Chapter logic
50. Redox balancing becomes easy once you track three things together: atoms, charge, and:
- A. Electron count (Correct)
- B. Temperature
- C. Volume
- D. Color
Explanation: Electron balance is the extra condition that defines redox balancing.
Electrode basics
51. An electrode where oxidation occurs is called:
- A. Anode (Correct)
- B. Cathode
- C. Salt bridge
- D. Electrolyte
Explanation: Oxidation occurs at anode in both galvanic and electrolytic cells.
Electrode basics
52. An electrode where reduction occurs is called:
- A. Cathode (Correct)
- B. Anode
- C. Bridge
- D. Junction
Explanation: Reduction occurs at the cathode.
Galvanic cell
53. In a galvanic cell, electrons flow externally from:
- A. Anode to cathode (Correct)
- B. Cathode to anode
- C. Salt bridge to electrode
- D. Electrolyte to wire
Explanation: Oxidation at anode releases electrons.
Galvanic cell
54. In a Daniell cell, zinc acts as:
- A. Anode (Correct)
- B. Cathode
- C. Salt bridge
- D. Electrolyte
Explanation: Zinc is oxidised to Zn$^{2+}$.
Galvanic cell
55. In a Daniell cell, copper acts as:
- A. Cathode (Correct)
- B. Anode
- C. Salt bridge
- D. Reducing agent
Explanation: Cu$^{2+}$ is reduced to copper metal.
Salt bridge
56. Main function of the salt bridge is to:
- A. Maintain electrical neutrality (Correct)
- B. Supply electrons
- C. Increase voltage directly
- D. Act as catalyst
Explanation: It allows ion migration to prevent charge buildup.
Salt bridge
57. A salt bridge usually contains:
- A. Inert electrolyte (Correct)
- B. Strong oxidising agent
- C. Only distilled water
- D. Molten metal
Explanation: It should not react with either half-cell.
Cell notation
58. In cell notation, the single vertical line represents:
- A. Phase boundary (Correct)
- B. Electron flow
- C. Salt bridge
- D. Reaction completion
Explanation: Single line separates different phases.
Cell notation
59. In cell notation, the double vertical line represents:
- A. Salt bridge (Correct)
- B. Oxidation step
- C. Reduction step
- D. Temperature barrier
Explanation: Double line denotes the liquid junction or bridge.
Oxidation-reduction
60. At the zinc electrode in Daniell cell, the half-reaction is:
- A. $Zn \to Zn^{2+}+2e^-$ (Correct)
- B. $Zn^{2+}+2e^- \to Zn$
- C. $Cu^{2+}+2e^- \to Cu$
- D. $Cu \to Cu^{2+}+2e^-$
Explanation: Zinc undergoes oxidation.
Oxidation-reduction
61. At the copper electrode in Daniell cell, the half-reaction is:
- A. $Cu^{2+}+2e^- \to Cu$ (Correct)
- B. $Cu \to Cu^{2+}+2e^-$
- C. $Zn^{2+}+2e^- \to Zn$
- D. $Zn \to Zn^{2+}+2e^-$
Explanation: Copper(II) is reduced.
Electron accounting
62. Electrons never pass through the salt bridge because they move through:
- A. External wire (Correct)
- B. Electrolyte directly
- C. Gas phase
- D. Solvent only
Explanation: The salt bridge carries ions, not electrons.
Ion migration
63. In a Daniell cell, anions from salt bridge migrate toward the:
- A. Anode compartment (Correct)
- B. Cathode compartment
- C. Wire
- D. Voltmeter
Explanation: Oxidation produces excess positive charge there.
Ion migration
64. Cations from salt bridge migrate toward the:
- A. Cathode compartment (Correct)
- B. Anode compartment
- C. External circuit
- D. Metal strip
Explanation: Reduction consumes cations, leaving excess anions behind.
Cell emf
65. Cell emf is equal to:
- A. $E_{cathode}-E_{anode}$ (Correct)
- B. $E_{anode}-E_{cathode}$
- C. Sum of oxidation potentials only
- D. Always positive 1 V
Explanation: Standard cell potential is cathode minus anode.
Standard potential
66. The standard hydrogen electrode is assigned potential:
- A. 0 V (Correct)
- B. 1 V
- C. -1 V
- D. Depends on acid
Explanation: SHE is the universal reference.
SHE
67. Standard conditions for SHE include hydrogen gas at:
- A. 1 bar (Correct)
- B. 10 bar
- C. 0.1 bar
- D. Any pressure
Explanation: Standard electrode potentials are measured under standard conditions.
SHE
68. The concentration of H$^+$ in SHE is:
- A. 1 M (Correct)
- B. 0.1 M
- C. 10 M
- D. Neutral water
Explanation: Standard solution concentration is 1 M.
Oxidising strength
69. A species with higher standard reduction potential is generally a stronger:
- A. Oxidising agent (Correct)
- B. Reducing agent
- C. Electrolyte
- D. Ligand
Explanation: It more readily gets reduced.
Reducing strength
70. A metal with very negative standard reduction potential is generally a stronger:
- A. Reducing agent (Correct)
- B. Oxidising agent
- C. Buffer
- D. Adsorbent
Explanation: It easily loses electrons.
Spontaneity
71. A galvanic cell reaction is spontaneous when cell emf is:
- A. Positive (Correct)
- B. Negative
- C. Zero
- D. Infinite
Explanation: Positive emf indicates spontaneous electrical work output.
Corrosion link
72. Rusting of iron is an example of:
- A. Electrochemical oxidation (Correct)
- B. Reduction only
- C. Neutralisation only
- D. Sublimation
Explanation: Corrosion is a redox process involving local cells.
Battery idea
73. A battery is essentially:
- A. A collection of electrochemical cells (Correct)
- B. A salt bridge only
- C. A capacitor only
- D. A catalyst pack
Explanation: It converts chemical energy to electrical energy.
NEET trap
74. In any electrochemical cell, oxidation occurs at anode whether the cell is:
- A. Galvanic or electrolytic (Correct)
- B. Only galvanic
- C. Only electrolytic
- D. Only Daniell type
Explanation: Anode/cathode are defined by reaction type, not sign alone.
Chapter logic
75. The fastest way to decode a cell question is to identify electron source, electron sink, and:
- A. Direction of ion migration (Correct)
- B. Atomic mass
- C. Color change only
- D. Boiling point
Explanation: That trio makes most cell setups clear.
Electrolysis
76. Electrolysis is a process driven by:
- A. Electrical energy (Correct)
- B. Only heat
- C. Only light
- D. Only pressure
Explanation: An external source forces a non-spontaneous reaction.
Faraday law
77. Faraday's first law states deposited mass is proportional to:
- A. Charge passed (Correct)
- B. Resistance
- C. Voltage only
- D. Time only
Explanation: More charge means more substance deposited.
Faraday law
78. Charge is related to current and time by:
- A. $Q=It$ (Correct)
- B. $Q=I/t$
- C. $Q=VIt$
- D. $Q=Rt$
Explanation: This is the basic electrical relation.
Faraday constant
79. One faraday corresponds to charge of approximately:
- A. 96500 C (Correct)
- B. 8.314 C
- C. 6.022 C
- D. 1 C
Explanation: It is the charge carried by one mole of electrons.
Faraday law
80. One mole of Ag$^+$ requires how many moles of electrons for deposition?
- A. 1 (Correct)
- B. 2
- C. 3
- D. 0.5
Explanation: Ag$^+ + e^- \to Ag$.
Faraday law
81. One mole of Cu$^{2+}$ requires how many moles of electrons for deposition?
- A. 2 (Correct)
- B. 1
- C. 3
- D. 4
Explanation: Cu$^{2+}+2e^-\to Cu$.
Mass deposition
82. Equivalent mass of a metal is molar mass divided by:
- A. Number of electrons exchanged (Correct)
- B. Density
- C. Atomic number
- D. Charge passed
Explanation: Equivalent mass is based on electron-change requirement.
Mass deposition
83. Mass deposited is proportional to equivalent mass and:
- A. Charge passed (Correct)
- B. Potential difference only
- C. Temperature only
- D. Molarity only
Explanation: Faraday's law combines these two.
Nernst idea
84. The Nernst equation links electrode potential with:
- A. Concentration or reaction quotient (Correct)
- B. Molar mass only
- C. Bond enthalpy
- D. pH only
Explanation: Potential changes with composition away from standard state.
Nernst sign
85. If reaction quotient increases for a galvanic cell reaction, cell emf generally:
- A. Decreases (Correct)
- B. Increases
- C. Stays constant
- D. Becomes infinite
Explanation: Higher Q reduces driving force in the Nernst equation.
Concentration cell
86. A concentration cell generates emf because the two half-cells have:
- A. Different ion concentrations (Correct)
- B. Different temperatures only
- C. Different metals only
- D. Different masses only
Explanation: The tendency is to equalise concentration.
Concentration cell
87. In a metal-ion concentration cell, the more dilute side usually acts as:
- A. Anode (Correct)
- B. Cathode
- C. Salt bridge
- D. Voltmeter
Explanation: Oxidation there raises ion concentration.
Conductance
88. Conductance is the reciprocal of:
- A. Resistance (Correct)
- B. Resistivity
- C. Current
- D. Voltage
Explanation: $G=1/R$.
Resistance
89. The SI unit of resistance is:
- A. Ohm (Correct)
- B. Siemens
- C. Volt
- D. Henry
Explanation: Resistance is measured in ohms.
Conductance unit
90. The SI unit of conductance is:
- A. Siemens (Correct)
- B. Ohm
- C. Volt
- D. Farad
Explanation: Conductance is measured in siemens or ohm$^{-1}$.
Specific conductance
91. Conductivity depends on the geometry-corrected conductance of:
- A. A solution column (Correct)
- B. A metal bar only
- C. A gas tube only
- D. A crystal lattice only
Explanation: It is a property of the solution, not of the cell dimensions.
Molar conductivity
92. Molar conductivity is conductivity multiplied by:
- A. 1000 divided by molarity (Correct)
- B. Molarity divided by 1000
- C. Density only
- D. Resistance only
Explanation: For molarity in mol L$^{-1}$, $\Lambda_m = \kappa \times 1000 / C$.
Strong electrolytes
93. Molar conductivity of strong electrolytes on dilution:
- A. Increases slightly (Correct)
- B. Decreases sharply
- C. Becomes zero
- D. Remains exactly constant
Explanation: Interionic interactions decrease on dilution.
Weak electrolytes
94. Molar conductivity of weak electrolytes on dilution:
- A. Increases sharply (Correct)
- B. Decreases
- C. Remains fixed
- D. Becomes negative
Explanation: Ionisation rises strongly with dilution.
Kohlrausch law
95. Kohlrausch's law is especially useful for finding limiting molar conductivity of:
- A. Weak electrolytes (Correct)
- B. Only metals
- C. Only strong acids
- D. Only nonelectrolytes
Explanation: It allows indirect estimation by ionic contributions.
Faraday numerics
96. If 2 faradays of charge pass through CuSO$_4$ solution, moles of Cu deposited are:
- A. 1 (Correct)
- B. 2
- C. 0.5
- D. 4
Explanation: Cu$^{2+}$ needs 2 electrons per atom.
Faraday numerics
97. If 96500 C pass through AgNO$_3$ solution, moles of Ag deposited are:
- A. 1 (Correct)
- B. 2
- C. 0.5
- D. 96500
Explanation: One faraday deposits one mole of Ag.
Cell potential
98. At equilibrium, cell emf becomes:
- A. Zero (Correct)
- B. Positive maximum
- C. Negative maximum
- D. Equal to 1 V
Explanation: No net driving force remains.
Chapter logic
99. Electrochemistry becomes easy once you separate questions into cells, electrolysis, or:
- A. Conductance branch (Correct)
- B. Mole concept branch
- C. Quantum branch
- D. Solid state branch
Explanation: These are the three main problem clusters.
Chapter logic
100. The single safest electrochemistry habit is to keep track of electrons, charge passed, and:
- A. n-factor or electron requirement per ion (Correct)
- B. Color of solution
- C. Atomic radius
- D. Hybridisation
Explanation: That prevents most numerical mistakes.
Mixed drill
101. In a galvanic cell, the anode is the electrode of:
- A. Oxidation (Correct)
- B. Reduction
- C. Neutralisation
- D. Hydration
Explanation: Anode is defined by oxidation.
Mixed drill
102. In electrolysis of molten NaCl, sodium forms at the:
- A. Cathode (Correct)
- B. Anode
- C. Salt bridge
- D. Wire junction
Explanation: Na$^+$ is reduced at the cathode.
Mixed drill
103. A species with more positive reduction potential is more easily:
- A. Reduced (Correct)
- B. Oxidised
- C. Hydrolysed
- D. Adsorbed
Explanation: Higher reduction potential means greater reduction tendency.
Mixed drill
104. The maximum electrical work from a galvanic cell is associated with:
- A. Positive emf (Correct)
- B. Negative emf
- C. Zero emf
- D. Infinite resistance
Explanation: Only a positive emf can drive spontaneous work.
Mixed drill
105. If current is doubled while time is halved, charge passed becomes:
- A. Unchanged (Correct)
- B. Doubled
- C. Halved
- D. Quadrupled
Explanation: Q = It remains the same.
Mixed drill
106. In a solution cell, conductivity generally increases when ion concentration initially:
- A. Increases (Correct)
- B. Decreases
- C. Becomes zero
- D. Matches pH
Explanation: More ions usually carry more current, especially in moderate concentration ranges.
Mixed drill
107. If one mole of Al$^{3+}$ is fully reduced to Al, the moles of electrons required are:
- A. 3 (Correct)
- B. 1
- C. 2
- D. 6
Explanation: Al$^{3+}+3e^-\to Al$.
Mixed drill
108. The mass deposited on electrolysis depends directly on charge passed and:
- A. Equivalent mass (Correct)
- B. Molar conductivity
- C. Cell constant
- D. pH
Explanation: This is Faraday's first law in usable form.
Mixed drill
109. The purpose of a porous partition or salt bridge is mainly to stop direct mixing while allowing:
- A. Ion migration (Correct)
- B. Electron flow through solution
- C. Pressure equalisation only
- D. Heat storage
Explanation: It keeps the circuit chemically and electrically workable.
Mixed drill
110. In Daniell cell, loss of mass occurs at:
- A. Zinc electrode (Correct)
- B. Copper electrode
- C. Salt bridge
- D. Both electrodes equally
Explanation: Zinc dissolves as Zn$^{2+}$.
Mixed drill
111. Gain of mass occurs at:
- A. Copper electrode (Correct)
- B. Zinc electrode
- C. Anode always
- D. Salt bridge
Explanation: Copper is deposited on the cathode.
Mixed drill
112. In a concentration cell with same metal electrodes, the dilute half-cell acts as anode because it tends to:
- A. Increase its ion concentration by oxidation (Correct)
- B. Lose ions by reduction
- C. Lower its concentration further
- D. Stop the reaction
Explanation: The cell works to remove the concentration difference.
Mixed drill
113. At 25$^\circ$C, the Nernst equation shows cell emf depends logarithmically on:
- A. Reaction quotient (Correct)
- B. Molar mass
- C. Resistance only
- D. Salt bridge length
Explanation: Composition enters through Q.
Mixed drill
114. The best quick predictor of spontaneity in a cell question is the sign of:
- A. $E_{cell}$ (Correct)
- B. Resistance
- C. Current
- D. Cell constant
Explanation: Positive cell emf means spontaneous galvanic behavior.
Mixed drill
115. The cell notation $Zn|Zn^{2+}||Cu^{2+}|Cu$ represents oxidation at:
- A. Zinc side (Correct)
- B. Copper side
- C. Salt bridge
- D. Both equally
Explanation: Left side in standard notation is usually the anode.
Mixed drill
116. The same notation represents reduction at:
- A. Copper side (Correct)
- B. Zinc side
- C. Salt bridge
- D. External wire
Explanation: Right side is the cathode in standard cell notation.
Mixed drill
117. One faraday deposits 0.5 mol of a divalent metal because:
- A. Two electrons are needed per metal ion (Correct)
- B. Half the atoms are lost
- C. Current is halved
- D. Voltage doubles
Explanation: Faraday counts moles of electrons.
Mixed drill
118. For the same quantity of electricity, the largest deposited mass comes from the ion with greatest:
- A. Equivalent mass (Correct)
- B. Atomic number
- C. Reduction potential
- D. Concentration only
Explanation: Mass deposited is proportional to equivalent mass.
Mixed drill
119. Corrosion can be slowed by preventing contact of metal with:
- A. Moisture and oxygen (Correct)
- B. Sunlight only
- C. Salt bridge only
- D. Voltage only
Explanation: These help create and sustain corrosion cells.
Mixed drill
120. Galvanisation protects iron mainly by coating it with:
- A. Zinc (Correct)
- B. Copper
- C. Silver
- D. Lead
Explanation: Zinc acts as sacrificial metal.
Mixed drill
121. In electroplating, the object to be plated is usually made the:
- A. Cathode (Correct)
- B. Anode
- C. Salt bridge
- D. Electrolyte
Explanation: Metal cations reduce onto the object surface.
Mixed drill
122. The plating metal is often made the anode so that it can:
- A. Replenish metal ions in solution (Correct)
- B. Stop current flow
- C. Act as salt bridge
- D. Lower conductivity
Explanation: Its oxidation balances the ion loss during plating.
Mixed drill
123. The most common NEET error in electrolysis is using current instead of charge. The correct bridge is:
- A. $Q=It$ (Correct)
- B. $Q=V/R$
- C. $Q=nRT/P$
- D. $Q=mc\Delta T$
Explanation: Always convert current and time into total charge first.
Mixed drill
124. The cleanest electrochemistry map is: identify oxidation/reduction, locate anode/cathode, then use emf or Faraday logic depending on whether the problem is about:
- A. Cells or electrolysis (Correct)
- B. Orbitals or spectra
- C. Acids or bases
- D. Adsorption or catalysis
Explanation: That split determines the right equation family.
Chapter integration
125. Electrochemistry is easiest to master when seen as one connected story of redox, electron flow, and:
- A. Quantitative charge accounting (Correct)
- B. Only memorised cell diagrams
- C. Boiling-point changes
- D. Molecular orbital theory
Explanation: Charge bookkeeping unifies cell, electrolysis, and conductance numericals.

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