Redox reactions, a shortened form of “reduction-oxidation” reactions, are fundamental to many chemical processes. From the rusting of iron to the metabolism of food in our bodies, redox reactions are omnipresent. As NEET aspirants, understanding this topic is pivotal. To aid in your preparations, we’ve put together a set of 20 MCQs on redox reactions. Let’s dive in!
1. Which of the following reactions is a redox reaction?
Answer:
Explanation:
In b), H2 is oxidized to H2O, and O2 is reduced to H2O. In c), C is oxidized to CO2.
2. In the reaction 2Al + 3Br2 → 2AlBr3, which species is oxidized?
Answer:
Explanation:
Al loses electrons and forms Al3+ in AlBr3, hence it is oxidized.
3. The oxidation number of hydrogen in H2O2 is:
Answer:
Explanation:
In H2O2, hydrogen has an oxidation number of -1.
4. What is the oxidizing agent in the reaction: 2H2S + O2 → 2H2O + 2S?
Answer:
Explanation:
O2 is reduced to H2O, making it the oxidizing agent.
5. In a redox reaction, the substance that gains electrons is said to be:
Answer:
Explanation:
Reduction is the gain of electrons.
6. The oxidation number of sulfur in SO4^2- is:
Answer:
Explanation:
Considering the oxidation numbers of oxygen (-2), sulfur in SO4^2- has an oxidation number of +6.
7. An increase in oxidation number indicates:
Answer:
Explanation:
An increase in oxidation number signifies the loss of electrons, which is oxidation.
8. In the reaction Zn + 2HCl → ZnCl2 + H2, which species is the reducing agent?
Answer:
Explanation:
Zn is oxidized to Zn2+ and thus, it is the reducing agent.
9. Which of the following is NOT a redox reaction?
Answer:
Explanation:
There is no change in oxidation states for any of the elements in the reaction.
10. The sum of the oxidation numbers in a neutral compound is always:
Answer:
Explanation:
The sum of oxidation numbers in a neutral compound is always zero.
11. Which of the following is an example of a disproportionation reaction?
Answer:
Explanation:
In the given reaction, oxygen is both oxidized and reduced.
12. Oxidation is always accompanied by:
Answer:
Explanation:
In every redox reaction, when one substance is oxidized, another is reduced.
13. The oxidation state of oxygen in OF2 is:
Answer:
Explanation:
Oxygen is in a higher oxidation state in OF2 compared to its usual state of -2.
14. What is the oxidation state of Cr in K2Cr2O7?
Answer:
Explanation:
Considering the oxidation numbers of oxygen (-2) and potassium (+1), chromium in K2Cr2O7 has an oxidation state of +6.
15. Which of the following species act as both oxidizing and reducing agents?
Answer:
Explanation:
Hydrogen peroxide can either gain or lose electrons, making it both an oxidizing and reducing agent.
16. The species that is reduced in a redox reaction is known as:
Answer:
Explanation:
The species that undergoes reduction (i.e., gains electrons) is the oxidizing agent or oxidant.
17. The oxidation state of Fe in Fe3O4 is:
Answer:
Explanation:
Fe3O4 is a mixed oxide with Fe in both +2 and +3 oxidation states.
18. Which process is responsible for the rusting of iron?
Answer:
Explanation:
Rusting involves the oxidation of iron and the reduction of oxygen.
19. In the redox reaction: MnO4^- + 8H+ + 5e^- → Mn2+ + 4H2O, the manganese is:
Answer:
Explanation:
The oxidation number of Mn decreases from +7 to +2, indicating reduction.
20. The oxidation state of carbon in methane (CH4) is:
Answer:
Explanation:
In methane, carbon has an oxidation state of -4.