Group 1: +1; Group 2: +2; p-block shows variable states: e.g. group 13 +1/+3, group 14 -4/+2/+4, group 15 -3/+3/+5, group 16 -2/+4/+6, group 17 -1/+1/+3/+5/+7.
-- NCERT Class 11 Chemistry, Ch. 3, p. 92Valence Oxidation States
8 MCQs9-step worked example
Source: NCERT Classification of Elements and Periodicity in PropertiesOfficial key: NTA-verifiedLast updated: 24 Sep 2026
Valence Oxidation States, explained for NEET
Valence is the combining capacity of an element — the number of bonds it can form. Oxidation state is the charge an atom would carry if all bonds were treated as fully ionic. These two concepts overlap but are not identical, and NEET exploits this gap.
Key distinction: Valence is always a positive whole number (or zero). Oxidation state can be positive, negative, or zero, and can be fractional in certain compounds (e.g., Fe₃O₄ gives Fe an average oxidation state of +8/3).
Periodic trends in valence:
- Across a period (left → right), valence with respect to hydrogen increases from 1 to 4 (Na to Si), then valence with respect to oxygen continues to increase while hydrogen valence decreases (P shows valence 3 with H but 5 with O).
- Group valence equals group number for s- and p-block elements (with respect to oxygen). For hydrogen compounds, valence = 8 − group number (for groups 15–17).
Variable oxidation states are characteristic of transition metals (d-block) because of the small energy gap between (n−1)d and ns electrons. Both sets participate in bonding. Example: Mn shows oxidation states from +2 to +7.
Watch-out for NEET: When a question asks "valence of nitrogen in NH₃," the answer is 3 (bonds formed). When it asks "oxidation state of nitrogen in NH₃," the answer is −3. Students who conflate the two lose marks on straightforward recall questions.
NCERT Class 11 Chemistry Chapter 3, page 95 lists representative oxidation states across periods and groups (NCERT Class 11 Chemistry Chapter 3).
Can you answer these Valence Oxidation States MCQs?
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
MCQ 1Easy RecallPractice
The valence of phosphorus in PCl₅ is:
Show answer and why every option is right or wrong
Answer: D. Valence is the combining capacity (number of bonds formed). In PCl₅, phosphorus forms 5 bonds, so valence = 5. Valence carries no sign. (NCERT Class 11 Chemistry Chapter 3, page 95.)
Why A is wrong: A is wrong because valence is not expressed with a + or − sign. '+5' is an oxidation state notation, not valence.
Why B is wrong: B is wrong because 3 is the valence of phosphorus in PCl₃, not PCl₅. In PCl₅, all five 3s and 3p + one promoted 3d electron participate in bonding.
Why C is wrong: C is wrong because valence is never negative. −5 would be an oxidation state (and not even correct for PCl₅).
MCQ 2Direct ApplicationPractice
The oxidation state of sulphur in Na₂S₂O₃ is:
Show answer and why every option is right or wrong
Answer: D. Let oxidation state of S = x. In Na₂S₂O₃: 2(+1) + 2x + 3(−2) = 0 → 2 + 2x − 6 = 0 → x = +2. (NCERT Class 11 Chemistry Chapter 3, page 95.)
Why A is wrong: A is wrong because +4 is the oxidation state of S in SO₂, not Na₂S₂O₃. A common error is confusing thiosulphate with sulphite.
Why B is wrong: B is wrong because +6 is the oxidation state of S in SO₄²⁻ or Na₂SO₄. Students who assume maximum oxidation state pick this.
Why C is wrong: C is wrong because +5 results from an arithmetic error (e.g., forgetting that there are two S atoms in the formula).
MCQ 3Easy RecallPractice
Which of the following statements about valence is correct?
Show answer and why every option is right or wrong
Answer: A. Valence represents combining capacity and is always expressed as a positive whole number (or zero). It does not carry a sign. (NCERT Class 11 Chemistry Chapter 3, page 95.)
Why B is wrong: B is wrong because valence has no sign — it is a magnitude only. Sign is associated with oxidation state, not valence.
Why C is wrong: C is wrong because valence and oxidation state differ. Example: N in NH₃ has valence 3 but oxidation state −3. They coincide only in specific cases.
Why D is wrong: D is wrong because nitrogen shows valence 3 in NH₃ and NF₃ but valence 5 in N₂O₅. Variable valence exists.
MCQ 4Direct ApplicationPractice
The oxidation state of Mn in KMnO₄ is:
Show answer and why every option is right or wrong
Answer: B. In KMnO₄: +1 + x + 4(−2) = 0 → x = +7. Mn exhibits its highest common oxidation state in permanganate. (NCERT Class 11 Chemistry Chapter 3, page 95.)
Why A is wrong: A is wrong because +4 is the oxidation state of Mn in MnO₂, not KMnO₄. Students confuse permanganate with manganese dioxide.
Why C is wrong: C is wrong because +6 is the oxidation state of Mn in manganate ion (MnO₄²⁻), not permanganate (MnO₄⁻). One oxygen or charge difference changes the answer.
Why D is wrong: D is wrong because +2 is the oxidation state of Mn in MnCl₂ or Mn²⁺ ion. This is the most stable state of Mn but not what KMnO₄ contains.
MCQ 5Direct ApplicationPractice
The oxidation state of Fe in Fe₃O₄ is:
Show answer and why every option is right or wrong
Answer: C. Fe₃O₄ is a mixed oxide (FeO·Fe₂O₃). Average oxidation state: 3x + 4(−2) = 0 → x = +8/3. This is a fractional average — the compound actually contains Fe²⁺ and Fe³⁺ ions. (NCERT Class 11 Chemistry Chapter 3, page 95.)
Why A is wrong: A is wrong because +2 is only the oxidation state of one Fe atom (in the FeO portion). The question asks for the oxidation state of Fe in the compound Fe₃O₄ as a whole, which yields a fractional average.
Why B is wrong: B is wrong because +3 is only the oxidation state of two Fe atoms (in the Fe₂O₃ portion). The average across all three Fe atoms is +8/3.
Why D is wrong: D is wrong because +4 results from incorrectly assigning oxygen a charge other than −2, or from an arithmetic error in the charge balance.
MCQ 6Easy RecallPractice
Which of the following elements shows only one oxidation state in all its compounds?
Show answer and why every option is right or wrong
Answer: B. Fluorine, being the most electronegative element, always shows an oxidation state of −1 in its compounds (it never exhibits a positive oxidation state). All other options show variable oxidation states. (NCERT Class 11 Chemistry Chapter 3, page 95.)
Why A is wrong: A is wrong because iron shows multiple oxidation states: +2 (ferrous) and +3 (ferric) are both common, plus others in complex compounds.
Why C is wrong: C is wrong because sulphur shows oxidation states of −2, +4, and +6 (e.g., H₂S, SO₂, H₂SO₄ respectively).
Why D is wrong: D is wrong because manganese shows oxidation states ranging from +2 to +7 (e.g., MnCl₂ is +2, KMnO₄ is +7).
MCQ 7Concept TrapPractice
The valence of carbon in CH₄ and CO₂ respectively are:
Show answer and why every option is right or wrong
Answer: C. Valence = number of bonds formed. In CH₄, carbon forms 4 single bonds (valence 4). In CO₂, carbon forms 2 double bonds = 4 bonds total (valence 4). Valence is the same in both. (NCERT Class 11 Chemistry Chapter 3, page 95.)
Why A is wrong: A is wrong because in CO₂, carbon forms 4 bonds (two double bonds = 4 bond pairs), not 2. Students who count double bonds as single units get this wrong.
Why B is wrong: B is wrong because valence never carries a sign. −4 and +4 are oxidation states, not valence values.
Why D is wrong: D is wrong because valence never carries a sign. Writing '+4' mixes up valence with oxidation state notation.
MCQ 8Concept TrapPractice
Transition metals exhibit variable oxidation states primarily because:
Show answer and why every option is right or wrong
Answer: A. The small energy gap between (n−1)d and ns electrons means both sets can participate in bond formation, allowing multiple oxidation states. (NCERT Class 11 Chemistry Chapter 3, page 95.)
Why B is wrong: B is wrong because large atomic radius affects reactivity and metallic character but does not directly explain why multiple oxidation states exist. The key factor is orbital energy proximity.
Why C is wrong: C is wrong because transition metals have partially filled d-orbitals (not completely filled). Elements with completely filled d-orbitals (like Zn) show limited variable oxidation states.
Why D is wrong: D is wrong because colour arises from d-d transitions and is a consequence of partially filled d-orbitals, not a cause of variable oxidation states. This reverses cause and effect.
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How do you solve a Valence Oxidation States question? A worked example
- 1
Given
Compound: K₂Cr₂O₇. Known oxidation states: K = +1, O = −2.
- 2
Required
Oxidation state of Cr.
- 3
Concept
In a neutral compound, the sum of all oxidation states equals zero. Assign known oxidation states to K and O, then solve for Cr algebraically.
- 4
Formula
Sum of oxidation states = 0 → 2(+1) + 2(x) + 7(−2) = 0
- 5
Substitution
2 + 2x − 14 = 0
- 6
Calculation
2x = 12 → x = +6
Note: The integers 2, 7, 14, and 12 appearing in this calculation are stoichiometric coefficients and arithmetic results — exact by definition. They do not limit significant figures. - 7
Final answer
Oxidation state of Cr in K₂Cr₂O₇ = +6.
- 8
Common trap
Students sometimes divide the total positive charge requirement by the wrong number of Cr atoms. With 2 Cr atoms, the total charge on Cr must be +12 (to balance +2 from K and −14 from O), giving +6 per atom. Dividing by 7 (number of oxygens) instead gives a nonsensical answer.
- 9
Similar NEET-style question
"What is the oxidation state of S in Na₂S₄O₆ (sodium tetrathionate)?" Apply the same charge-balance method: 2(+1) + 4x + 6(−2) = 0 → x = +2.5. This tests comfort with fractional oxidation states — a common NEET twist.
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What to remember before solving Valence Oxidation States questions
More in Classification of Elements and Periodicity in Properties: 4 exam traps and mistakes · 1 formula · 1 question pattern from its other lessons.
Valence Oxidation States questions from past NEET papers
No question in our NEET 2020–2025 set targets this topic directly.
All 10 past-paper questions from Classification of Elements and Periodicity in Properties →
Sources
NCERT refs: Class 11 Chemistry Chapter 3, p.95
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
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