Oxidation number (also called oxidation state) is the hypothetical charge an atom would carry if every bond it forms were treated as fully ionic, with each shared electron pair assigned entirely to the more electronegative partner. NCERT fixes it with a short set of rules: an atom in its free, elemental form is assigned oxidation number zero; a monatomic ion's oxidation number equals its charg
Redox Reactions
Class 116 previous-year questions from this chapter every option and the correct answer, free · where the marks are
1. Oxidation number and balancing redox equations
Exam focus: Oxygen isn't always −2: it's −1 in peroxides (H₂O₂), −1/2 in superoxides (KO₂), and +2 in OF₂, where fluorine is the more electronegative atom — NEET tests exactly these exceptions, not the default. Also watch for disproportionation, where the same element is simultaneously oxidised and reduced in one reaction, such as Cl₂ with cold dilute NaOH.
Redox Reactions: Oxidation Number and Balancing
NEET Adda247
Full-chapter one-shot including oxidation-number rules and both balancing methods; also covers other redox subtopics.
ChemistryNEET 2025show ▾Consider the following compounds: , and . The oxidation states of the underlined elements (O in , O in , S in ) in them are, respectively:
- A.+1, –1 and +6✓
- B.+2, –2 and +6
- C.+1, –2 and +4
- D.+4, –4 and +6
Solution
In the superoxide ion gives oxygen each, i.e. K is (the element asked); in oxygen is ; in sulphur is . Matching the underlined elements gives .
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Save for spaced revision (free account)ChemistryNEET 2023show ▾On balancing the given redox reaction,
the coefficients , and are found to be, respectively:
- A.1, 3, 8✓
- B.3, 8, 1
- C.1, 8, 3
- D.8, 1, 3
The worked solution is part of a paid pack.
ChemistryNEET 2020show ▾What is the change in the oxidation number of carbon in the following reaction?
- A.+4 to +4
- B.0 to +4
- C. to +4✓
- D.0 to
The worked solution is part of a paid pack.
2. Types of redox reactions
Exam focus: Whether one species can oxidise another is decided by E°cell = E°(reduction of the oxidiser) − E°(reduction of the reducing agent) coming out positive — that's how "will X displace Y" questions are actually meant to be solved, not from a memorised reactivity list. Disproportionation (one element both oxidised and reduced) and its reverse, comproportionation, are the classification names NEET most often asks you to apply correctly.
Types of Redox Reactions
PW English Medium
Full-chapter one-shot covering combination/decomposition/displacement/disproportionation reactions among other redox topics.
ChemistryNEET 2024show ▾Which reaction is not a redox reaction?
- A.
- B.
- C.✓
- D.
Solution
is a double displacement (precipitation) with no change in any oxidation number. The other three involve electron transfer.
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Save for spaced revision (free account)ChemistryNEET 2021show ▾Which of the following reactions is a metal displacement reaction? Choose the right option.
ChemistryNEET 2019show ▾Which of the following reactions are disproportionation reactions?
(a)
(b)
(c)
(d)
Select the correct option:
- A.(a) and (b) only✓
- B.(a), (b) and (c)
- C.(a), (c) and (d)
- D.(a) and (d) only
The worked solution is part of a paid pack.