MCQs — Electrochemistry

Practice questions for Chemistry.

← Back to Electrochemistry

Question 101

In the reaction 2Na + Cl2 -> 2NaCl, sodium is functioning as the:

A. Oxidizing agent, since it is itself reduced

B. Reducing agent, since it is itself oxidized

C. Neither an oxidizing nor a reducing agent

D. A spectator species only

Question 102

In the same reaction (2Na + Cl2 -> 2NaCl), chlorine is functioning as the:

A. Reducing agent, since it is itself oxidized

B. Oxidizing agent, since it is itself reduced

C. Neither an oxidizing nor a reducing agent

D. A spectator species only

Question 103

The first step in identifying the oxidizing and reducing agents in a chemical reaction is to:

A. Guess which substance seems more reactive

B. Work out the oxidation states of all the elements involved in the reaction

C. Measure the reaction's temperature

D. Determine the physical states of all substances

Question 104

Once oxidation states are assigned, the element showing an INCREASE in oxidation state is being oxidized. The reactant containing this element is therefore identified as the:

A. Oxidizing agent

B. Reducing agent

C. Spectator species

D. Catalyst

Question 105

Once oxidation states are assigned, the element showing a DECREASE in oxidation state is being reduced. The reactant containing this element is therefore identified as the:

A. Reducing agent

B. Oxidizing agent

C. Spectator species

D. Catalyst

Question 106

The oxidizing or reducing agent in a reaction is identified as the whole molecule or formula unit, rather than just the specific atom that changes oxidation state, because:

A. Only isolated atoms can ever react, never whole molecules

B. Entire substances react with each other, so the whole reactant containing the changing atom is what actually functions as the agent

C. Oxidation states only apply to isolated atoms, not molecules

D. This is simply an arbitrary naming convention with no real basis

Question 107

In Fe2O3 + 3CO -> 2Fe + 3CO2, the oxidation state of carbon increases from +2 (in CO) to +4 (in CO2). This means CO is:

A. Being reduced, so CO functions as the oxidizing agent

B. Being oxidized, so CO functions as the reducing agent

C. Unchanged throughout the reaction

D. Acting as a spectator species

Question 108

In the same reaction (Fe2O3 + 3CO -> 2Fe + 3CO2), the oxidation state of iron decreases from +3 (in Fe2O3) to 0 (in Fe). This means Fe2O3 is:

A. Being oxidized, so Fe2O3 functions as the reducing agent

B. Being reduced, so Fe2O3 functions as the oxidizing agent

C. Unchanged throughout the reaction

D. Acting as a spectator species

Question 109

In the reaction WO3 + 3H2 -> W + 3H2O, tungsten's oxidation state decreases from +6 (in WO3) to 0 (in W). This means WO3 functions as the:

A. Reducing agent, since tungsten is being oxidized

B. Oxidizing agent, since tungsten is being reduced

C. Neither agent, since tungsten is unaffected

D. Spectator species

Question 110

In the same reaction (WO3 + 3H2 -> W + 3H2O), hydrogen's oxidation state increases from 0 (in H2) to +1 (in H2O). This means H2 functions as the:

A. Oxidizing agent, since hydrogen is being reduced

B. Reducing agent, since hydrogen is being oxidized

C. Neither agent, since hydrogen is unaffected

D. Spectator species

Question 111

Tungsten is extracted from tungsten(VI) oxide using hydrogen gas mainly because:

A. Hydrogen acts as a reducing agent capable of removing oxygen from (reducing) the tungsten oxide, leaving pure tungsten metal

B. Hydrogen is simply an inert carrier gas with no chemical role

C. Tungsten oxide is naturally unstable and decomposes on its own

D. Hydrogen acts as an oxidizing agent in this reaction

Question 112

Comparing Fe2O3 + 3CO -> 2Fe + 3CO2 and WO3 + 3H2 -> W + 3H2O, what role do both reactions share in common?

A. In both, a metal oxide is reduced to the pure metal by a reducing agent (CO or H2) that itself becomes oxidized

B. In both, the metal oxide acts as the reducing agent

C. In both, no redox process actually occurs

D. In both, the pure metal product is further oxidized afterward

Question 113

When acidified potassium permanganate (KMnO4) solution is added to a solution containing a reducing agent, its purple colour:

A. Intensifies further

B. Is discharged, turning colorless

C. Turns bright yellow

D. Remains completely unchanged

Question 114

The purple colour of potassium permanganate disappears when it reacts with a reducing agent such as iron(II) sulfate because:

A. The purple permanganate ion is reduced to the pale/colorless manganese(II) ion as it oxidizes the reducing agent

B. Potassium permanganate simply evaporates during the reaction

C. Iron(II) sulfate is colorless and cancels out the purple color physically

D. No actual chemical reaction is occurring

Question 115

During the reaction between potassium permanganate and a reducing agent, the oxidation number of manganese changes from:

A. +2 to +7

B. +7 to +2

C. 0 to +7

D. +7 to 0

Question 116

When an acidified hydrogen peroxide solution is added to a potassium iodide solution, the solution's colour changes to:

A. Bright blue

B. Reddish-brown, due to the formation of iodine

C. Pale green

D. Completely colorless

Question 117

In the reaction between potassium iodide and acidified hydrogen peroxide, potassium iodide is functioning as the reducing agent because:

A. It gains electrons as iodide ions are converted into iodine

B. It loses electrons (is oxidized) as iodide ions are converted into iodine

C. It remains completely unchanged throughout the reaction

D. It acts only as a spectator ion

Question 118

Is hydrogen peroxide functioning as an oxidizing agent or a reducing agent when it reacts with potassium iodide?

A. A reducing agent, since it is itself oxidized

B. An oxidizing agent, since it is itself reduced as it oxidizes the iodide ions to iodine

C. Neither; hydrogen peroxide does not participate in electron transfer here

D. Both simultaneously, in equal measure

Question 119

A color change occurring during a chemical reaction, such as purple turning colorless or colorless turning reddish-brown, is often used as practical evidence that a reaction is:

A. A purely physical change with no chemical significance

B. A redox (oxidation-reduction) reaction

C. Never actually a genuine chemical reaction

D. An acid-base neutralization only

Question 120

Potassium permanganate and hydrogen peroxide are often used specifically to test for the presence of reducing agents in a solution because:

A. They undergo a clear, visible color change upon being reduced, providing an easily observable confirmation that a reducing agent was present and reacted with them

B. They never actually react with reducing agents

C. They change color regardless of what is added to them

D. They can only be used in solid form, never in solution

🎯 How to get the most out of these questions

Attempt each question before revealing the answer.
Read the explanation even when you answered correctly — it reinforces the concept.
Note down any question you got wrong and revisit it the next day.
Use the pagination below the list to work through every page — do not stop at page 1.

📌 MCQs — FAQs

Are answers included for every question in this section?

Yes — each published question includes an answer. Explanations are shown where they have been added.

Can I print these questions?

Yes — use your browser's print option (Ctrl+P / Cmd+P) to print or save the page as PDF.

How often are questions updated?

New questions are added regularly. If a paper pattern changes, existing questions are reviewed and updated.