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Oxidation State - (Concept)

One of the notable features of transition elements is the great variety of oxidation states these may show in their compounds.
The elements which give the greatest number of oxidation states occur in or near the middle of the series. Manganese, for example, exhibits all the oxidation states from +2 to +7. The lesser number of oxidation states at the extreme ends stems from either too few electrons to lose or share (Sc, Ti) or too many d electrons (hence fewer orbitals available in which to share electrons with others) for higher valence (Cu, Zn). Thus, early in the series scandium(II) is virtually unknown and titanium (IV) is more stable than Ti(III) or Ti(II). At the other end, the only oxidation state of zinc is +2 (no d electrons are involved). The maximum oxidation states of reasonable stability correspond in value to the sum of the s and d electrons upto manganese (Ti^IV O₂, V^VO₂⁺, Cr^V1O₄^2–, Mn^VIIO₄^–) followed by a rather abrupt decrease in stability of higher oxidation states, so that the typical species to follow are Fe^II,III, Co^II,III, Ni^II, Cu^I,II, Zn^II.
The variability of oxidation states, a characteristic of transition elements, arises out of incomplete filling of d orbitals in such a way that their oxidation states differ from each other by unity, e.g., V^II, V^III,V^IV, V^V. This is in contrast with the variability of oxidation states of non transition elements where oxidation states normally differ by a unit of two.
An interesting feature in the variability of oxidation states of the d–block elements is noticed among the groups. Although in the p–block the lower oxidation states are favoured by the heavier members (due to inert pair effect), the opposite is true in the groups of d-block. For example, in group 6, Mo(VI) and W(VI) are found to be more stable than Cr(VI). Thus Cr(VI) in the form of dichromate in acidic medium is a strong oxidising agent, whereas MoO₃ and WO₃ are not.
Low oxidation states are found when a complex compound has ligands capable of π-acceptor character in addition to the σ-bonding. For example, in Ni(CO)₄ and Fe(CO)₅, the oxidation state of nickel and iron is zero.

Question

Asked in: JEE Main 2014-2014

Which one of the following exhibits the largest number of oxidation states?

A.	Ti (22)
B.	V(23)
C.	Cr (24)
D.	Mn (25)

Question

Asked in: JEE Main 2019-2019

The element that usually does NOT show variable oxidation states is:

A.	V
B.	Sc
C.	Cu
D.	Ti

Question

Asked in: JEE Main 2019-2019

The metal that gives hydrogen gas upon treatment with both acid, as well as base, is :

A.	Zinc
B.	Iron
C.	Mercury
D.	Magnesium

Question

Asked in: JEE Main 2021-2021

The electrode potential of $M^{2+}/M$ 3-d series elements shows the positive value for:

A.	Co
B.	Fe
C.	Cu
D.	Zn

Question

Asked in: JEE Main 2021-2021

$\mathrm{Fex_2\textup{ and }Fey_3}$ are known when x and y are:

A.	x = Cl, Br and y = F, Cl , Br, I
B.	x = Cl, Br and y = F, Cl , Br
C.	x = F, Cl, Br and y = F, Cl , Br, I
D.	x = F, Cl, Br, I and y = F, Cl , Br, I

Question

Asked in: JEE Main 2021-2021

The common positive oxidation states for an element with atomic number 24, are :

A.	+1 and +3
B.	+1 to +6
C.	+1 and +3 to +6
D.	+2 to +6

Question

Asked in: JEE Main 2020-2020

The oxidation states of transition metal atoms in $K_{2}Cr_{2}O_{7} , KMnO_{4}$ and $K_{2}FeO_{4}$ , respectively are X, Y and Z , the sum of X, Y and Z is ___________

A.	19
B.	-
C.	-
D.	-

Question

Asked in: JEE Main 2022-2022

Among the following which is the strongest oxidizing agent?

A.	$\mathrm{Mn}^{3+}$
B.	$\mathrm{Fe}^{3+}$
C.	$\mathrm{Ti}^{3+}$
D.	$\mathrm{Cr}^{3+}$

Question

Asked in: JEE Main 2021-2021

The correct order of following $3 \mathrm{d}$ metal oxides, according to their oxidation numbers is :

$\mathrm{(a) CrO _{3}\ \ (b) Fe _{2} O _{3}\ \ (c) MnO _{2}\ \ (d) V _{2} O _{5}\ \ (e) Cu _{2} O}$

A.	$(\mathrm{d})>(\mathrm{a})>(\mathrm{b})>(\mathrm{c})>(\mathrm{e})$
B.	$(a) >(\mathrm{c})>(\mathrm{d})>(\mathrm{b})>(\mathrm{e})$
C.	$(a) >(\mathrm{d})>(\mathrm{c})>(\mathrm{b})>(\mathrm{e})$
D.	$(\mathrm{c})>(\mathrm{a})>(\mathrm{d})>(\mathrm{e})>(\mathrm{b})$

Question

Asked in: JEE Main 2021-2021

The nature of oxides $\mathrm{V}_{2} \mathrm{O}_{3}$ and $\mathrm{CrO}$ is indexed as $' \mathrm{X}^{\prime}$ and ' $\mathrm{Y} \: '$ type respectively. The correct set of $X$ and $Y$ is :

A.	$X=acidic$ $Y=acidic$
B.	$X=basic$ $Y=amphoteric$
C.	$X=basic$ $Y=basic$
D.	$X=amphoteric$ $Y=basic$

Question

Asked in: BITSAT-2018

Which of the following arrangements does not represent the correct order of the property stated against it ?

A.	$Sc < Ti < Cr < Mn:$ number of oxidation states
B.	$V^{2+} < Cr^{2+} < Mn^{2+} < Fe^{2+}$ : paramagnetic behaviour
C.	$Ni^{2+}<Co^{2+}<Fe^{2+}<Mn^{2+}:$ ionic size
D.	$Co^{3+}<Fe^{3+}<Cr^{3+}<Sc^{3+}:$ stability in aqueous solution

Question

Asked in: BITSAT-2018

Iron exhibits + 2 and +3 oxidation states. Which of the following statements about iron is incorrect ?

A.	Ferrous oxide is more basic in nature than the ferric oxide.
B.	Ferrous compounds are relatively more ionic than the corresponding ferric compounds
C.	Ferrous compounds are less volatile than the corresponding ferric compounds.
D.	Ferrous compounds are more easily hydrolysed than the corresponding ferric compounds.

Question

Asked in: JEE Main 2022-2022

The spin-only magnetic moment value of $\mathrm{\mathrm{M}^{3+} ion }$ (in gaseous state) from the pairs $\mathrm{\mathrm{Cr}^{3+} / \mathrm{Cr}^{2+}, \mathrm{Mn}^{3+} / \mathrm{Mn}^{2+}, \mathrm{Fe}^{3+} / \mathrm{Fe}^{2+} \text { and } \mathrm{Co}^{3+} / \mathrm{Co}^{2+}}$ that has negative standard electrode potential, is ____ B.M. [Nearest integer]

A.	4
B.	-
C.	-
D.	-

Question

Finely divided iron combines with CO to give

A.	$\mathrm{\operatorname{Fe}(C O)_{5}}$
B.	$\mathrm{Fe _{2}( CO )_{9}}$
C.	$\mathrm{F e_{2}(C O)_{12}}$
D.	$\mathrm{F e(C O)_{6}}$

Question

Asked in: JEE Main 2017-2017

Which of the following ions does not liberate hydrogen gas in reaction with dilute acids?

A.	Ti²⁺
B.	V²⁺
C.	Cr²⁺
D.	Mn²⁺

Question

Asked in: JEE Main 2013-2013

The element with which of the following outer electron configuration may exhibit the largest number of oxidation states in its compounds :

A.	$3d^{5}4s^{2}$
B.	$3d^{8}4s^{2}$
C.	$3d^{7}4s^{2}$
D.	$3d^{6}4s^{2}$

Question

Asked in: JEE Main 2009-2009

In context with the transition elements, which of the following statements is incorrect ?

A.	In addition to the normal oxidation states, the zero oxidation state is also shown by these elements in complexes.
B.	In the highest oxidation states, the transition metals show basic character and form cationic complexes.
C.	In the highest oxidation states of the first five transition elements (Sc to Mn), all the 4s and 3d electrons are used for bonding.
D.	Once the d⁵ configuration is exceeded, the tendency to involve all the 3d electrons in bonding decreases.

Question

Asked in: JEE Main 2004-2004

Of the following outer electronic configurations of atoms, the highest oxidation state is achieved by which one of them?

A.	$(n-1)d^{8}ns^{2}$
B.	$(n-1)d^{5}ns^{1}$
C.	$(n-1)d^{3}ns^{2}$
D.	$(n-1)d^{5}ns^{2}$

Question

Asked in: JEE Main 2003-2003

The number of $d$ - electrons retained in $Fe^{2+}$ $(At.\; no.\; Fe=26)$ ions is

A.	3
B.	4
C.	5
D.	6

Question

Asked in: NEET 2015-2015

The number of d-electrons in Fe²⁺(Z = 26) is not equal to the number of electrons in which one of the following ?

A.	d - electrons in Fe (Z = 26)
B.	p - electrons in Ne (Z = 10)
C.	s - electrons in Mg (Z = 12)
D.	p - electrons in CI (Z =17)

Question

Asked in: JEE Main-2023

Which one amongst the following are good oxidizing agents?

$\text { (A) } \mathrm{Sm}^{2+} \text { (B) } \mathrm{Ce}^{2+} \text { (C) } \mathrm{Ce}^{4+} \text { (D) } \mathrm{Tb}^{4+}$

Choose the most appropriate answer from the options given below:

A.	D only
B.	C only
C.	C and D only
D.	A and B only

Question

Asked in: JEE Main-2023

The set of correct statements is :

(i) Manganese exhibits +7 oxidation state in its oxide.

(ii) Ruthenium and Osmium exhibit +8 oxidation in their oxides.

(iii) Sc shows +4 oxidation state which is oxidizing in nature.

(iv) Cr shows oxidising nature in +6 oxidation state.

A.	(ii) and (iii)
B.	(i), (ii) and (iv)
C.	(ii), (iii) and (iv)
D.	(i) and (iii)

Question

Asked in: JEE Main-2023

The correct order of basicity of oxides of vanadium is

A.	$\mathrm{V}_{2} \mathrm{O}_{5}>\mathrm{V}_{2} \mathrm{O}_{4}>\mathrm{V}_{2} \mathrm{O}_{3}$
B.	$\mathrm{V}_{2} \mathrm{O}_{4}>\mathrm{V}_{2} \mathrm{O}_{3}>\mathrm{V}_{2} \mathrm{O}_{5}$
C.	$\mathrm{V}_{2} \mathrm{O}_{3}>\mathrm{V}_{2} \mathrm{O}_{5}>\mathrm{V}_{2} \mathrm{O}_{4}$
D.	$\mathrm{V}_{2} \mathrm{O}_{3}>\mathrm{V}_{2} \mathrm{O}_{4}>\mathrm{V}_{2} \mathrm{O}_{5}$

Question

Asked in: JEE Main-2023

Highest oxidation state of $\mathrm{Mn}$ is exhibited in $\mathrm{Mn}_2 \mathrm{O}_7$ . The correct statements about $\mathrm{Mn}_2 \mathrm{O}_7$ are
(A) $\mathrm{Mn}$ is tetrahedrally surrounded by oxygen atoms.
(B) $\mathrm{Mn}$ is octahedrally surrounded by oxygen atoms.
(C) Contains Mn-O-Mn bridge.
(D) Contains Mn-Mn bond.
Choose the correct answer from the options given below:

A.	A and Conly
B.	A and D only
C.	B and C only
D.	B and D only

Question

Asked in: JEE Main-2023

In ammonium – phosphomolybdate, the oxidation state of Mo is + _______

A.	6
B.	-
C.	-
D.	-

Question

Asked in: JEE Main-2023

In chromyl chloride, the number of d-electrons present on chromium is same as in (Given at no. of Ti : 22, V : 23, Cr : 24, Mn : 25, Fe : 26)

A.	Fe (III)
B.	V (IV)
C.	Ti (III)
D.	Mn (VII)

Question

Asked in: JEE Main-2023

Which halogen is known to cause the reaction given below:

$2 \mathrm{Cu}^{2+}+4 \mathrm{X}^{-} \rightarrow \mathrm{Cu}_2 \mathrm{X}_2(\mathrm{~s})+\mathrm{X}_2$

A.	All halogens
B.	Only chlorine
C.	Only Bromine
D.	Only Iodine

Question

Asked in: JEE Main-2023

The sum of oxidation state of the metals in $\mathrm{Fe}(\mathrm{CO})_5, \mathrm{VO}^{2+}$ and $\mathrm{WO}_3$ is___________

A.	10
B.	-
C.	-
D.	-

Question

Asked in: JEE Main-2023

Which of the following statements are correct ?

(A) The $\mathrm{M}^{3+} / \mathrm{M}^{2+}$ reduction potential for iron is greater than manganese
(B) The higher oxidation states of first row d-block elements get stabilized by oxide ion.
(C) Aqueous solution of $\mathrm{Cr}^{2+}$ can liberate hydrogen from dilute acid.
(D) Magnetic moment of $\mathrm{V}^{2+}$ is observed between 4.4-5.2 BM.

Choose the correct answer from the options given below:

A.	(C), (D) only
B.	(B), (C) only
C.	(A), (B), (D) only
D.	(A), (B) only

Question

Why copper utensils become green if not cleaned for a long period of time?

A.	Formation of copper hydroxide on the surface.
B.	Formation of copper sulphate on the surface.
C.	Formation of copper oxide on the surface.
D.	Formation of copper carbonate on the surface.

Question

A metal X is not affected by acidic or alkaline conditions but blackens in air if kept for prolonged time. Its bromide is used extensively in photography. What is the X?

A.	$Ag$
B.	$Au$
C.	$Cd$
D.	$Pt$

Question

Calomel on reaction with ammonium hydroxide produces a corrosive white solid X and another white solid Y. Y is reacted with CaO to obtain pungent gas Z. What is X, Y and Z?

A.	$X=NH_{2}HgCl,Y=NH_{4}Cl,Z=NH_{3}$
B.	$X=NH_{2}Cl,Y=NH_{2}HgCl,Z=NH_{3}$
C.	$X=NH_{4}Cl,Y=Hg_{2}Cl_{2},Z=NH_{3}$
D.	$X=Hg_{2}Cl_{2},Y=NH_{4}Cl,Z=NH_{3}$

Question

A brown compound X of Mn is reacted with HCl which releases a gas Y. Y is reacted with Excess $NH_{3}$ to give an oily explosive liquid Z. What is X, Y and Z?

A.
B.	$X=Mn_{3}O_{4},Y=Cl_{2},Z=NCl_{3}$
C.	$X=MnO_{2},Y=Cl_{2},Z=NCl_{2}$
D.	$X=Mn_{3}O_{4},Y=NCl_{3},Z=Cl_{2}$

Question

A blue transition metal salt X reacts with $H_{2}S$ in acidic medium and gives a black precipitate Y, which is insoluble in aqueous solution of $KOH$ . The same salt on reacting with KI in acidic medium produces a yellow solution and a white precipitate Z. What is X, Y and Z?

A.
B.	$X=CuSO_{4}\; Y=CuS \; Z=Cul_{2}$
C.	$X=CuS\; Y=CuCl_{2} \; Z=Cu_{2}l_{2}$
D.	$X=CuSO_{4}\; Y=CuS_{2} \; Z=Cu_{2}l_{2}$

Question

Which sulphide of the following transition metals is white?

A.	ZnS
B.	MnS
C.	CuS
D.	AgS

Question

Platinum dissolves in NOCL to give _________.

A.	$\mathrm{PtNO_3}$
B.	$\mathrm{Pt(NO_3)_2}$
C.	$\mathrm{(NO^{+})_2[PtCl_6]^{2-}}$
D.	$\mathrm{PtCl _4}$

Question

$\mathrm{FeCl_2\: in \: HCl \: and \: HNO_3}$ mixture gives_______.

A.	$\mathrm{FeO}$
B.	$\mathrm{Fe_2O_3}$
C.	$\mathrm{FeCl_2.H_2O}$
D.	$\mathrm{FeCl_3}$

Question

A solution contains $\mathrm{Fe^{2+}\: and \: Zn^{2+}}$ ions. What can be done to separate them?

A.	The mixture cannot be separated.
B.	Dissolve in acid.
C.	Dissolve in base.
D.	Pass $\mathrm{H_2S}$ Gas.

Question

On reacting $\mathrm{MnO_2}$ with $\mathrm{NaI}$ in presence of acid, two solids A and B are formed along with a violet gas C. What is A, B and C?

A.	$\mathrm{A: MnI \: B: NaO \: C: O_2}$
B.	$\mathrm{A: MnSO_4\: B: NaO\: C: O_2}$
C.	$\mathrm{A: MnI_2 \: B: NaO\: C: I_2}$
D.	$\mathrm{A: MnSO_4\: B: Na_2SO_4 \: C: I_2}$

Question

When Sodium bromide is reacted with silver nitrate a pale-yellow solid is formed that is photosensitive and dissolves in ammonium hydroxide with difficulty. What is the compound?

A.	$\mathrm{AgCl}$
B.	$\mathrm{NaNO_3}$
C.	$\mathrm{AgBr}$
D.	$\mathrm{NaCl}$

Question

$\mathrm{MnO_2}$ reacts with $\mathrm{NaCl}$ in acidic medium to release a pungent green-coloured gas A that reacts with excess $\mathrm{NH_3}$ to give an oily explosive liquid B. What is A and B?

A.	$\mathrm{Cl_2, NO_2}$
B.	$\mathrm{HCl, NCl_3}$
C.	$\mathrm{HCl, NO_2}$
D.	$\mathrm{Cl_2, NCl_3}$

Question

What angle is form by Mn-O-Mn in $\mathrm{Mn}_2 \mathrm{O}_7$ ?

A.	$120^{\circ}$
B.	$130^{\circ}$
C.	$110^{\circ}$
D.	$180^{\circ}$

Question

$\mathrm{Mn}_2 \mathrm{O}_7$ reacts with $\mathrm{H}_2 \mathrm{O}_2$ in presence of sulfuric acid to give a pale blue gas with a strong smell that acts as a strong oxidising agent. What is the gas?

A.	$\mathrm{Cl}_2$
B.	$\mathrm{O}_2$
C.	$\mathrm{O}_3$
D.	$\mathrm{HCl}$

Question

Why gadolinium has an abnormally low third ionisation enthalpy?

A.	because of the small size of Gd.
B.	Because of the less shielding of 5f-orbitals
C.	Because of stable configuration.
D.	All of the above.

Question

Match the following correctly:

Metal	Process
I. Fe	A. Ziegler-Natta catalyst
II.Ni	B. Wacker process
III. Ti	C. Hydrogenation of fats.
IV. Pd	D. Haber process

A.	I-D, II-C, III-A, IV-B
B.	I-A, II-B, III-D, IV-C
C.	I-C, II-D, III-A, IV-B
D.	I-A, II-D, III-C, IV-B

Question

How many of the following divalent ions have a magnetic moment of $\sqrt{35}$ Bohr Magnetons?

$\mathrm{Mn}^{2+}$ $\mathrm{Zn}^{2+}$ ${Ni}^{2+}$ $\mathrm{Sc}^{3+}$

A.	1
B.	-
C.	-
D.	-

Question

Asked in: JEE Main-2024

Which of the following statements is not correct about rusting of iron?

A.	Coating of iron surface by tin prevents rusting, even if the tin coating is peeling off.
B.	When pH lies above 9 or 10, rusting of iron does not take place.
C.	Dissolved acidic oxides $\mathrm{SO}_2, \mathrm{NO}_2$ in water act as catalyst in the process of rusting
D.	Rusting of iron is envisaged as setting up of electrochemical cell on the surface of iron object.

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