Why do transition elements exhibit their highest oxidation states only in their oxides and fluorides?

Why do transition elements exhibit their highest oxidation states only in their oxides and fluorides? +

Correct Answer

Transition metals show their highest oxidation states mainly in oxides and fluorides because O and F are highly electronegative and form very strong bonds with the metal, stabilising the metal in a very high positive oxidation state.

Detailed Explanation

Transition elements have electrons in both (n−1)d and ns orbitals. Therefore, several oxidation states are possible. However, very high oxidation states are difficult to stabilise because they involve removal or effective use of a large number of electrons. Oxygen and fluorine overcome this difficulty because they are highly electronegative elements.

High oxidation state + highly electronegative ligand → stable compound

1. Oxygen is highly electronegative
Oxygen forms strong bonds with transition metals. It can stabilise metals in high oxidation states through strong M–O bonding. Example:

Mn⁺⁷ in Mn₂O₇

2. Fluorine is the most electronegative element
Fluorine strongly attracts electron density from the transition metal and therefore stabilises very high positive oxidation states. Example:

Pt⁺⁶ in PtF₆

3. Strong bond formation provides stability
The high oxidation state is stabilised by strong metal–oxygen or metal–fluorine bonds. This is why the highest oxidation states are generally observed in compounds containing O or F, rather than with less electronegative ligands such as Cl⁻, Br⁻ or I⁻.

Important Examples

Element	High Oxidation State	Example
Mn	+7	Mn2O7, KMnO4
Cr	+6	CrO3, Cr2O72−
V	+5	V2O5
Pt	+6	PtF6

JEE / NEET Shortcut

Remember:

Highest oxidation state → stabilised by O and F

Reason:

O, F → high electronegativity + strong M–O/M–F bonds → high oxidation-state stability

Exam point: This does not mean that high oxidation states are literally impossible with every other ligand; rather, the highest oxidation states are especially stabilised and commonly observed with oxides and fluorides.

30 Related MCQs with Solutions

1. Why are high oxidation states of transition metals stabilised by fluorine?

A. Fluorine is electropositive

B. Fluorine is highly electronegative

C. Fluorine has low ionization energy

D. Fluorine is a metal

Answer: B
Fluorine strongly attracts electron density and stabilises high positive oxidation states.

2. Which two elements particularly stabilise high oxidation states of transition metals?

A. H and C

B. O and F

C. Cl and Br

D. S and I

Answer: B. O and F

3. The highest oxidation state of Mn is:

A. +2

B. +4

C. +6

D. +7

Answer: D. +7

4. Oxidation state of Mn in KMnO₄ is:

A. +2

B. +4

C. +6

D. +7

Answer: D. +7

5. Which compound contains Cr in +6 oxidation state?

A. CrCl₃

B. CrO₃

C. Cr₂O₃

D. CrCl₂

Answer: B. CrO₃

6. Which element is the most electronegative?

A. O

B. N

C. F

D. Cl

Answer: C. F

7. Strong M–O bonds help to:

A. Destabilise high oxidation states

B. Stabilise high oxidation states

C. Reduce electronegativity

D. Prevent oxidation

Answer: B

8. Which oxidation state of Mn is present in Mn₂O₇?

A. +4

B. +5

C. +6

D. +7

Answer: D. +7

9. Which compound contains V in its highest common oxidation state?

A. VO

B. V₂O₃

C. VO₂

D. V₂O₅

Answer: D. V₂O₅

10. High oxidation states are generally favoured by:

A. Weakly electronegative ligands

B. Highly electronegative ligands

C. Noble gases

D. Alkali metals

Answer: B

11. Which is the most electronegative halogen?

A. Cl

B. Br

C. I

D. F

Answer: D. F

12. PtF₆ contains platinum in oxidation state:

A. +2

B. +4

C. +5

D. +6

Answer: D. +6

13. Oxygen stabilises high oxidation states mainly because of its:

A. Low electronegativity

B. High electronegativity and strong bonding ability

C. Metallic character

D. Large atomic size

Answer: B

14. Which is a high oxidation state compound of chromium?

A. CrCl₂

B. CrCl₃

C. K₂Cr₂O₇

D. Cr₂O₃

Answer: C

15. In K₂Cr₂O₇, oxidation state of Cr is:

A. +3

B. +4

C. +5

D. +6

Answer: D. +6

16. Which factor is most important in stabilising a high oxidation state?

A. Strong metal-ligand bonding

B. Large atomic radius only

C. Low electronegativity of ligand

D. Inertness of ligand

Answer: A

17. Which ligand is particularly effective in stabilising very high oxidation states?

A. F⁻

B. I⁻

C. Br⁻

D. H₂

Answer: A. F⁻

18. Which is more electronegative?

A. O

B. F

C. S

D. Cl

Answer: B. F

19. Which transition metal oxide contains the metal in a very high oxidation state?

A. Mn₂O₇

B. FeO

C. NiO

D. CuO

Answer: A. Mn₂O₇

20. The oxidation state of Mn in MnO₄⁻ is:

A. +3

B. +5

C. +6

D. +7

Answer: D. +7

21. Which halogen is most capable of stabilising high oxidation states?

A. F

B. Cl

C. Br

D. I

Answer: A. F

22. Which property of F is mainly responsible for high oxidation-state stabilisation?

A. Low electronegativity

B. High electronegativity

C. Large size

D. Metallic nature

Answer: B

23. Which compound represents Mn in +7 oxidation state?

A. MnCl₂

B. MnO

C. MnO₂

D. KMnO₄

Answer: D

24. Why are chlorides generally less effective than fluorides in stabilising very high oxidation states?

A. Cl is less electronegative than F

B. Cl is a metal

C. F has lower electronegativity

D. Cl cannot form bonds

Answer: A

25. Which statement is correct?

A. High oxidation states are favoured by electropositive ligands

B. Highly electronegative ligands help stabilise high oxidation states

C. Fluorine always gives low oxidation states

D. Oxygen cannot stabilise high oxidation states

Answer: B

26. The highest oxidation state of Cr commonly observed is:

A. +2

B. +3

C. +6

D. +7

Answer: C. +6

27. The highest oxidation state of V is:

A. +2

B. +3

C. +4

D. +5

Answer: D. +5

28. Which pair correctly represents high oxidation states?

A. Mn(+7), Cr(+6)

B. Mn(+2), Cr(+2)

C. Fe(+2), Co(+2)

D. Ni(+1), Cu(+1)

Answer: A

29. High oxidation states of transition metals are commonly found in:

A. Oxides and fluorides

B. Iodides only

C. Bromides only

D. Sulfides only

Answer: A

30. The main reason for the stability of very high oxidation states in oxides and fluorides is:

A. Low electronegativity of O and F

B. High electronegativity and strong metal–ligand bonding

C. Large size of O and F

D. Metallic character of O and F

Answer: B

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