Statement-I: Oxidation number of $\mathrm{Ni}$ in $\left[\mathrm{Ni}(\mathrm{CO})_4\right]$ is $+2.$ Statement-II: Nickel is bonded to neutral ligand, carbonyl.

Both the statements are correct

Both the statements are incorrect

Statement-I is correct but statement-II is incorrect

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JEE • CHEMISTRY • REDOX REACTIONS

Redox reactions practice · Medium

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These sets use single-correct-answer MCQs. They do not cover every JEE Main or JEE Advanced question format and are not full-length mock papers.

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Showing 1-30 of 171 questions

1 Medium

1 of 171

Remembering +4 | -1

A reagent, which can decrease the oxidation number of an element, is called

View answer and explanation

Correct option: C

reducing agent

Option C (reducing agent) is correct because a reducing agent donates electrons, causing another substance to have its oxidation number decreased.

2 Medium

2 of 171

Analyzing +4 | -1

Consider the following decomposition reaction

2 \mathrm{KClO}_3 \longrightarrow 2 \mathrm{KCl}+3 \mathrm{O}_2

In the above reaction,

View answer and explanation

Correct option: B

chlorine is undergoing reduction

Option B is correct because chlorine's oxidation state decreases from +5 to -1, indicating reduction.

3 Medium

3 of 171

Analyzing +4 | -1

Assertion (A):

\mathrm{HNO}_3

acts as oxidizing agent.

Reason (R): Oxidation no. of nitrogen is +5, no increase in oxidation no. beyond +5 can occur. The oxidation no. of

\mathrm{HNO}_3

can only decrease.

View answer and explanation

Correct option: A

Both (A) & (R) are true and the (R) is the correct explanation of the (A)

The correct answer is A because HNO3 acts as an oxidizing agent due to the nitrogen atom's ability to decrease its oxidation number from +5, and the reason correctly explains this.

4 Medium

4 of 171

Application +4 | -1

The number of mole of ferrous oxalate oxidised by one mole of

\mathrm{KMn}{\mathrm{O}_4}

is:

View answer and explanation

Correct option: D

5/3

Option D (

5/3

) is correct because the balanced redox reaction between ferrous oxalate and KMnO4 requires 5/3 moles of ferrous oxalate per mole of KMnO4.

5 Medium

5 of 171

Analyzing +4 | -1

Which one is not a redox titration?

View answer and explanation

Correct option: D

\mathrm{AgN}{\mathrm{O}_3}vs.\mathrm{KCl}

The correct answer is D (AgNO₃ vs. KCl) because this is a precipitation reaction, not a redox reaction involving electron transfer.

6 Medium

6 of 171

Application +4 | -1

The average oxidation number of

{I}

{KI}_3

and

{Fe}

{Fe}_3 {O}_4

are respectively :-

View answer and explanation

Correct option: A

-1 / 3,+8 / 3

Option A (

-1 / 3,+8 / 3

) is correct because it represents the average oxidation states calculated for I in KI3 and Fe in Fe3O4 respectively.

7 Medium

7 of 171

Application +4 | -1

In compound

H{N_3}

(Hydrozoic acid), oxidation state of N atoms are

View answer and explanation

Correct option: B

0,-2,+1

Option B (0,-2,+1) is correct because the oxidation states of the three nitrogen atoms in

HN_3

are 0, -2, and +1, respectively, based on resonance structures.

8 Medium

8 of 171

Analyzing +4 | -1

Which of the following involves the reduction of copper?

View answer and explanation

Correct option: B

{Cu}^{2+}(\mathrm{aq})+2 {I^-}(\mathrm{aq}) \rightarrow 2 {CuI}(\mathrm{aq})

The correct answer is B because in the reaction Cu2+(aq) + 2I-(aq) → 2CuI(aq), copper's oxidation state decreases from +2 to +1, indicating reduction.

9 Medium

9 of 171

Application +4 | -1

Fe shows an oxidation state of +1 in:

View answer and explanation

Correct option: B

\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_5 \mathrm{NO}\right] \mathrm{SO}_4

Option B ([Fe(H₂O)₅NO]SO₄) is correct because the iron in this complex has an oxidation state of +1, considering NO as NO⁺.

10 Medium

10 of 171

Remembering +4 | -1

The redox reactions are called combustion reactions which make use of

View answer and explanation

Correct option: A

elemental dioxygen

Option A (elemental dioxygen) is correct because combustion reactions are redox reactions that involve the rapid reaction of a substance with oxygen.

11 Medium

11 of 171

Understanding +4 | -1

During a redox change, the oxidant

{\mathrm{K}_2}\mathrm{C}{\mathrm{r}_2}{\mathrm{O}_7}

is always reduced to :

View answer and explanation

Correct option: C

\mathrm{C}{\mathrm{r}^{3 + }}

Option C is correct. During a redox reaction, dichromate (K2Cr2O7) acts as an oxidizing agent and is reduced to Cr3+.

12 Medium

12 of 171

Analyzing +4 | -1

Assuming complete ionization, same moles of which of the following compounds will require the least
Amount of acidified

\mathrm{KMn}{\mathrm{O}_\mathrm{4}}

for complete oxidation?

View answer and explanation

Correct option: C

\mathrm{FeS}{\mathrm{O}_\mathrm{4}}

Option C (FeSO4) is correct because FeSO4 requires the least amount of KMnO4 for complete oxidation as it involves the smallest change in oxidation state.

13 Medium

13 of 171

Understanding +4 | -1

Which one of the following is the correct match?

View answer and explanation

Correct option: D

\mathrm{SO}_2

- both oxidising and reducing agent

Option D (SO2 - both oxidising and reducing agent) is correct because sulfur in SO2 has an intermediate oxidation state (+4) and can either gain or lose electrons.

14 Medium

14 of 171

Application +4 | -1

In the following redox reactions

C{r_2}O_7^{2 - } + F{e^{2 + }}\,\xrightarrow{\,}\,F{e^{3 + }} + C{r^{3 + }}

1 mole of

C{r_2}O_7^{2 - }

oxidises

View answer and explanation

Correct option: D

\mathrm{6\,\,moles\,\,of }\,\,F{e^{2 + }}

Option D (

\mathrm{6\,\,moles\,\,of }\,F{e^{2 + }}

) is correct because 1 mole of

C{r_2}O_7^{2 - }

requires 6 moles of

F{e^{2 + }}

for complete oxidation based on the balanced redox reaction.

15 Medium

15 of 171

Understanding +4 | -1

Which of the following acts as an oxidising as well as reducing agent?

View answer and explanation

Correct option: D

\mathrm{NaN}{\mathrm{O}_2}

The correct answer is D (

\mathrm{NaN}{\mathrm{O}_2}

) because it can both accept and donate electrons, acting as both an oxidizing and reducing agent due to nitrogen's intermediate oxidation state.

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16 Medium

16 of 171

Application +4 | -1

For the balanced redox reaction.

{aMnO}_4^{-}+{bH}_2 {O}_2+{cH}^{+} \rightarrow {dMn}^{2 +}+{eO}_2+{fH}_2 {O}

the value of

a, b, c

and

e

respectively are

View answer and explanation

Correct option: B

2,5,6,5

The correct answer is

2, 5, 6, 5

. Balancing the redox reaction requires determining the correct stoichiometric coefficients to ensure both mass and charge are conserved.

17 Medium

17 of 171

Analyzing +4 | -1

Assertion:

\mathrm{SO}_2

and

\mathrm{Cl}_2

both are bleaching agents.

Reason: Both are reducing agents.

View answer and explanation

Correct option: C

Assertion is true, Reason is false

Option C (Assertion is true, Reason is false) is correct because both SO2 and Cl2 are bleaching agents, but their mechanisms differ; SO2 acts as a reducing agent, while Cl2 acts as an oxidizing agent.

18 Medium

18 of 171

Analyzing +4 | -1

Which of the following would not give disproportionation reaction on hydrolysis?

View answer and explanation

Correct option: B

\mathrm{N}_2 \mathrm{O}_5

Option B is correct because N2O5, upon hydrolysis, only forms HNO3, where nitrogen remains in the +5 oxidation state, thus not undergoing disproportionation.

19 Medium

19 of 171

Analyzing +4 | -1

White phosphorus reacts with caustic soda, the products are

\mathrm{P}{\mathrm{H}_3}\,\mathrm{and}\,\mathrm{Na}{\mathrm{H}_2}\mathrm{P}{\mathrm{O}_2}.

This reaction is an example of

View answer and explanation

Correct option: C

Disproportionation

Option C is correct because phosphorus undergoes both oxidation and reduction in this reaction, which is the definition of a disproportionation reaction.

20 Medium

20 of 171

Application +4 | -1

In which of the following pairs, there is greatest difference in the oxidation number of the underlined elements?

View answer and explanation

Correct option: D

{\underline{\mathrm{S}}{O}_2}

and

{\underline{\mathrm{S}}{O}_3}

Option D (SO2 and SO3) is correct because the difference in oxidation numbers of S in SO2 and SO3 is 2, which is the greatest among the given pairs.

21 Medium

21 of 171

Application +4 | -1

The number of mole of potassium salt,

i.e,\mathrm{KH}{\mathrm{C}_2}{\mathrm{O}_4}\mathrm{.}{\mathrm{H}_2}{\mathrm{C}_2}{\mathrm{O}_4}.2{\mathrm{H}_2}\mathrm{O}

oxidised by one mole of permanganate ion is :

View answer and explanation

Correct option: D

5/4

Option D (

5/4

) is correct because it represents the number of moles of the potassium salt oxidized by one mole of permanganate ion based on the balanced redox reaction.

22 Medium

22 of 171

Analyzing +4 | -1

Which is the best description of the behaviour of bromine in the reaction given below ?

\mathrm{H}_2 \mathrm{O}+\mathrm{Br}_2 \longrightarrow \mathrm{HOBr}+\mathrm{HBr}

View answer and explanation

Correct option: D

Both oxidised and reduced

The correct answer is D because bromine undergoes both oxidation and reduction in the reaction, acting as both an oxidizing and reducing agent (disproportionation).

23 Medium

23 of 171

Analyzing +4 | -1

In the following chemical reaction:

{Ag}_2 {O}+{H}_2 {O}+2 e^{-} \rightarrow 2 {Ag}+2 {OH}^{-}

View answer and explanation

Correct option: C

Water is oxidised

Option C is correct because in the reaction, water gains oxygen, indicating it is being oxidized.

24 Medium

24 of 171

Application +4 | -1

The value of n in

\mathrm{MnO}_4^ - + 8{\mathrm{H}^ + } + n{e^ - } \to \mathrm{M}{\mathrm{n}^{2 + }} + 4{\mathrm{H}_2}\mathrm{O}

View answer and explanation

Correct option: A

Option A (5) is correct because the manganese oxidation state changes from +7 to +2, requiring 5 electrons to be added to the left side of the equation.

25 Medium

25 of 171

Analyzing +4 | -1

Which one of the following is an example of disproportionation reaction?

View answer and explanation

Correct option: A

3MnO_4^{2 - } + 4{H^ + } \to 2MnO_4^ - + Mn{O_2} + 2{H_2}O

Option A is correct because in the given reaction, MnO4^2- undergoes both oxidation and reduction, thus it is a disproportionation reaction.

26 Medium

26 of 171

Remembering +4 | -1

Which metal exhibits more than one oxidation states?

View answer and explanation

Correct option: D

\mathrm{Fe}

Option D (

\mathrm{Fe}

) is correct because iron (Fe) is a transition metal that commonly exhibits multiple oxidation states, such as +2 and +3.

27 Medium

27 of 171

Understanding +4 | -1

Statement-I: Oxidation number of

\mathrm{Ni}

\left[\mathrm{Ni}(\mathrm{CO})_4\right]

+2.

Statement-II: Nickel is bonded to neutral ligand, carbonyl.

View answer and explanation

Correct option: D

Statement-I is incorrect but statement-II is correct

The correct answer is D (Statement-I is incorrect but statement-II is correct) because the oxidation number of Ni in [Ni(CO)4] is 0, not +2, and CO is a neutral ligand.

28 Medium

28 of 171

Analyzing +4 | -1

In which transfer of five electrons takes place?

View answer and explanation

Correct option: A

\mathrm{MnO}_4^ - \to \mathrm{M}{\mathrm{n}^{2 + }}

Option A (

\mathrm{MnO}_4^ - \to \mathrm{M}{\mathrm{n}^{2 + }}

) is correct because the oxidation state of Mn changes from +7 to +2, involving a transfer of 5 electrons.

29 Medium

29 of 171

Application +4 | -1

Oxidation number of P in

{P_2}O_7^{4 - }

is :

View answer and explanation

Correct option: C

+ 5

Option C (

+ 5

) is correct because the oxidation number of P is calculated by setting up an equation based on the overall charge of the ion.

30 Medium

30 of 171

Analyzing +4 | -1

Assertion: Oxidation number of carbon in

\mathrm{HCHO}

is zero.

Reason:

\text{HCHO}

formaldehyde, is a covalent compound.

View answer and explanation

Correct option: B

Assertion is true, Reason is true and Reason is not correct explanation for Assertion

Option B is correct because both the assertion and reason are true, but the reason is not the correct explanation for the assertion. The oxidation number of carbon in HCHO is zero, and HCHO is a covalent compound, but the latter doesn't explain the former.

Revision notes and key takeaways

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Key Takeaways

✓ This set contains 171 single-correct-answer MCQs on REDOX REACTIONS.
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