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Explore popular questions from Redox Reactions for NEET. This collection covers Redox Reactions previous year NEET questions hand picked by experienced teachers.

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Redox Reactions

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Q 1. The brown ring complex is formulated as {tex} \left[ \mathrm { Fe } \left( \mathrm { H } _ { 2 } \mathrm { O } \right) _ { 5 } \mathrm { NO } \right] \mathrm { SO } _ { 4 } {/tex}. The oxidation number of iron is

1

B

2

C

3

D

0

Explanation

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Q 2. In which of the following reactions, there is no change in valency?

A

{tex} 4 \mathrm { KClO } _ { 3 } \rightarrow 3 \mathrm { KClO } _ { 4 } + \mathrm { KCl } {/tex}

B

{tex} \mathrm { SO } _ { 2 } + 2 \mathrm { H } _ { 2 } \mathrm { S } \rightarrow 2 \mathrm { H } _ { 2 } \mathrm { O } + 3 \mathrm { S } {/tex}

{tex} \mathrm { BaO } _ { 2 } + \mathrm { H } _ { 2 } \mathrm { SO } _ { 4 } \rightarrow \mathrm { BaSO } _ { 4 } + \mathrm { H } _ { 2 } \mathrm { O } _ { 2 } {/tex}

D

{tex} 2 \mathrm { BaO } + \mathrm { O } _ { 2 } \rightarrow 2 \mathrm { BaO } _ { 2 } {/tex}

Explanation

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Q 3. The oxidation state of chromium in the final product formed by the reaction between KI and acidified potassium dichromate solution is:

{tex} + 3 {/tex}

B

{tex} + 2 {/tex}

C

{tex} + 6 {/tex}

D

{tex} + 4 {/tex}

Explanation

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Q 4. In which of the following pairs, there is greatest difference in the oxidation number of the underlined elements?

A

{tex} \mathrm{ \underline { N}{O } _ { 2 }} {/tex} and {tex} \mathrm{ \underline { N } _ { 2 } { O } _ { 4 } }{/tex}

B

{tex} \underline { \mathrm { P } } _ { 2 } \mathrm { O } _ { 5 } {/tex} and {tex} \underline { \mathrm { P } } _ { 4 } \mathrm { O } _ { 10 } {/tex}

C

{tex} \mathrm{\underline { N } _ { 2 } O} {/tex} and {tex} \mathrm{ \underline { N }O } {/tex}

{tex} \mathrm{ \underline { S } O_ { 2 } }{/tex} and {tex} \mathrm{ \underline { S}O_3 }{/tex}

Explanation

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Q 5. A compound of {tex} \mathrm {Xe} {/tex} and {tex} \mathrm { F } {/tex} is found to have {tex} 53.5 \% {/tex} of {tex} \mathrm {Xe } {/tex} . What is oxidation number of {tex} \mathrm { Xe } {/tex} in this compound?

A

{tex} - 4 {/tex}

B

{tex}0{/tex}

C

{tex} + 4 {/tex}

{tex} + 6 {/tex}

Explanation

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Q 6. The reaction in which hydrogen peroxide acts as a reducing agent is

A

{tex} \mathrm { PbS } + 4 \mathrm { H } _ { 2 } \mathrm { O } _ { 2 } \rightarrow \mathrm { PbSO } _ { 4 } + 4 \mathrm { H } _ { 2 } \mathrm { O } {/tex}

B

{tex} 2 \mathrm { KI } + \mathrm { H } _ { 2 } \mathrm { O } _ { 2 } \rightarrow 2 \mathrm { KOH } + \mathrm { I } _ { 2 } {/tex}

C

{tex} 2 \mathrm { FeSO } _ { 4 } + \mathrm { H } _ { 2 } \mathrm { SO } _ { 4 } + \mathrm { H } _ { 2 } \mathrm { O } _ { 2 } \rightarrow \mathrm { Fe } _ { 2 } \left( \mathrm { SO } _ { 4 } \right) _ { 3 } + 2 \mathrm { H } _ { 2 } \mathrm { O } {/tex}

{tex} \mathrm { Ag } _ { 2 } \mathrm { O } + \mathrm { H } _ { 2 } \mathrm { O } _ { 2 } \rightarrow 2 \mathrm { Ag } + \mathrm { H } _ { 2 } \mathrm { O } + \mathrm { O } _ { 2 } {/tex}

Explanation

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Q 7. Of the following reactions, only one is a redox reaction. Identify it

A

{tex} \mathrm { Ca } ( \mathrm { OH } ) _ { 2 } + 2 \mathrm { HCl } \rightarrow \mathrm { CaCl } _ { 2 } + 2 \mathrm { H } _ { 2 } \mathrm { O } {/tex}

B

{tex} \mathrm { BaCl } _ { 2 } + \mathrm { MgSO } _ { 4 } \rightarrow \mathrm { BaSO } _ { 4 } + \mathrm { MgCl } _ { 2 } {/tex}

C

{tex} 2 \mathrm { S } _ { 2 } \mathrm { O } _ { 7 } ^ { 2 - } + 2 \mathrm { H } _ { 2 } \mathrm { O } \rightarrow 4 \mathrm { SO } _ { 4 } ^ { 2 - } + 4 \mathrm { H } ^ { + } {/tex}

{tex} \mathrm { Cu } _ { 2 } \mathrm { S } + 2 \mathrm { FeO } \rightarrow 2 \mathrm { Cu } + 2 \mathrm { Fe } + \mathrm { SO } _ { 2 } {/tex}

Explanation

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Q 8. Arrange the following in the order of their decreasing electrode potentials : {tex} \mathrm { Mg } , \mathrm { K } , \mathrm { Ba } {/tex} and {tex} \mathrm { Ca } {/tex}

A

{tex} \mathrm { K } > \mathrm { Ca } > \mathrm { Ba } > \mathrm { Mg } {/tex}

B

{tex} \mathrm { Ba } > \mathrm { Ca } > \mathrm { K } > \mathrm { Mg } {/tex}

C

{tex} \mathrm { Ca } > \mathrm { Mg } > \mathrm { K } > \mathrm { Ba } {/tex}

{tex} \mathrm { Mg } > \mathrm { Ca } > \mathrm { Ba } > \mathrm { K } {/tex}

Explanation

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Q 9. Which of the following statements are correct concerning redox properties?
(i) A metal {tex} \mathrm { M } {/tex} for which {tex} \mathrm { E } ^ { \circ } {/tex} for the half life reaction {tex} \mathrm { M } ^ { \mathrm { n } + } + \mathrm { ne } ^ { - } \rightleftharpoons \mathrm { M } {/tex} is very negative will be a good reducing agent.
(ii) The oxidizing power of the halogens decreases from chlorine to iodine.
(iii) The reducing power of hydrogen halides increases from hydrogen chloride to hydrogen iodide

(i), (ii) and (iii)

B

(i) and (ii)

C

(i) only

D

(ii) and (iii)

Explanation

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Q 10. A negative {tex} \mathrm { E } ^ { \circ } {/tex} means that redox couple is a {tex} \underline{\mathrm A} {/tex} than the {tex} \mathrm { H } ^ { + } / \mathrm { H } _ { 2 } {/tex} couple
A positive {tex} \mathrm { E } ^ { \circ } {/tex} means that the redox couple is a {tex} \underline {\mathrm { B }} {/tex} than {tex} \mathrm { H } ^ { + } / \mathrm { H } _ { 2 } {/tex} couple

A

{tex} \mathrm { A } = {/tex} stronger reducing agent
{tex} \mathrm { B } = {/tex} weaker reducing agent

B

{tex} \mathrm { A } = {/tex} stronger oxidising agent
{tex} \mathrm { B } = {/tex} weaker oxidising agent

C

{tex} \mathrm { A } = {/tex} weaker oxidising agent
{tex} \mathrm { B } = {/tex} stronger oxidising agent

Both (a) and (c)

Explanation

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Q 11. If equal volume of reactants are used, then no. of moles of {tex} \mathrm { KMnO } _ { 4 } {/tex} (moles per litre) used in acidic medium required to completely oxidise {tex} 0.5 \mathrm { M } \ \mathrm { FeSO } _ { 3 } ? {/tex} is

0.3

B

0.1

C

0.2

D

0.4

Explanation

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Q 12. If rod of a metal {tex} ( \mathrm { x } ) {/tex} is put in a metal ion solution which is blue in colour, solution turn colourless. The metal rod and solution respectively are?

A

Zinc and {tex} \mathrm { Cu } ( \mathrm { II } ) {/tex}

B

Zinc and {tex} \mathrm {{Ni}(II)}{/tex}

C

Aluminium and {tex}\mathrm {Cu (II)}{/tex}

Both (a) and (c)

Explanation

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Q 13. In the reaction between {tex} \mathrm { SO } _ { 2 } {/tex} and {tex} \mathrm { O } _ { 3 } {/tex} the equivalent weight of sulphur in product is

A

The same as its molecular weight

Half of the molecular weight

C

One-third of the molecular weight

D

One-fourth of the molecular weight

Explanation

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Q 14. When {tex} \mathrm { KMnO } _ { 4 } {/tex} reacts with acidified {tex} \mathrm { FeSO } _ { 4 } {/tex}

{tex} \mathrm { FeSO } _ { 4 } {/tex} is oxidised and {tex} \mathrm { KMnO } _ { 4 } {/tex} is reduced

B

only {tex} \mathrm { KMnO } _ { 4 } {/tex} is oxidised

C

only {tex} \mathrm { FeSO } _ { 4 } {/tex} is oxidised

D

None of these

Explanation


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Q 15. Consider the following reaction
{tex} \mathrm { xMnO } _ { 4 } ^ { - } + \mathrm { yC } _ { 2 } \mathrm { O } _ { 4 } ^ { 2 - } + \mathrm { zH } ^ { + } \rightarrow \mathrm { xMn } ^ { 2 + } + 2 \mathrm { yCO } _ { 2 } + \frac { \mathrm { Z } } { 2 } \mathrm { H } _ { 2 } \mathrm { O } {/tex}
The value's of x, yand z in the reaction are, respectively:

A

{tex} 5,2 {/tex} and {tex} 16 {/tex}

B

{tex} 2, 5 {/tex} and {tex} 8 {/tex}

{tex} 2, 5 {/tex} and {tex} 16 {/tex}

D

{tex} 5,2 {/tex} and {tex} 8 {/tex}

Explanation

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Q 16. When {tex} \mathrm { Cl } _ { 2 } {/tex} gas reacts with hot and concentrated sodium hydroxide solution, the oxidation number of chlorine changes from :

A

zero to {tex} + 1 {/tex} and zero to {tex} - 5 {/tex}

zero to {tex} - 1 {/tex} and zero to {tex} + 5 {/tex}

C

zero to {tex} - 1 {/tex} and zero to {tex} + 3 {/tex}

D

zero to {tex} + 1 {/tex} and zero to {tex} - 3 {/tex}

Explanation

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Q 17. Oxidation state for nitrogen is incorrectly given in

A

Compound - - oxidation state - {tex} \mathrm -3 {/tex}

B

Compound - - oxidation state - {tex} \mathrm -1 {/tex}

Compound - - oxidation state - {tex} \mathrm+2 {/tex}

D

Compound - - oxidation state -{tex} \mathrm-3{/tex}

Explanation


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Q 18. Standard electrode potentials of redox couples {tex} \mathrm { A } ^ { 2 + } / \mathrm { A } , \mathrm { B } ^ { 2 + } / \mathrm { B } , \mathrm { C } ^ { 2 + } / \mathrm { C } {/tex} and {tex} \mathrm { D } ^ { 2 + } / \mathrm { D } {/tex} are {tex} 0.3 \mathrm { V } , - 0.5 \mathrm { V } , - 0.75 \mathrm { V } {/tex} and {tex} 0.9 \mathrm { V } {/tex} respectively. Which of these is best oxidising agent and reducing agent respectively-

A

{tex} \mathrm {D ^ { 2 + } / D} {/tex} and {tex} \mathrm {B ^ { 2 + } / B} {/tex}

B

{tex} \mathrm { B } ^ { 2 + } / \mathrm { B } {/tex} and {tex} \mathrm { D } ^ { 2 + } / \mathrm { D } {/tex}

{tex} \mathrm { D } ^ { 2 + } / \mathrm { D } {/tex} and {tex} \mathrm { C } ^ { 2 + } / \mathrm { C } {/tex}

D

{tex} \mathrm { C } ^ { 2 + } / \mathrm { C } {/tex} and {tex} \mathrm { D } ^ { 2 + } / \mathrm { D } {/tex}

Explanation

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Q 19. {tex} \mathrm { MnO } _ { 4 } ^ { 2 - } {/tex} (1 mole) in neutral aqueous medium disproportionates to

{tex} 2 / 3 {/tex} mole of {tex} \mathrm { MnO } _ { 4 } ^ { - } {/tex} and {tex} 1 / 3 {/tex} mole of {tex} \mathrm { MnO } _ { 2 } {/tex}

B

{tex} 1 / 3 {/tex} mole of {tex} \mathrm { MnO } _ { 4 } ^ { - } {/tex} and {tex} 2 / 3 {/tex} mole of {tex} \mathrm { MnO } _ { 2 } {/tex}

C

{tex} 1 / 3 {/tex} mole of {tex} \mathrm { Mn } _ { 2 } \mathrm { O } _ { 7 } {/tex} and {tex} 1 / 3 {/tex} mole of {tex} \mathrm { MnO } _ { 2 } {/tex}

D

{tex} 2 / 3 {/tex} mole of {tex} \mathrm { Mn } _ { 2 } \mathrm { O } _ { 7 } {/tex} and {tex} 1 / 3 {/tex} mole of {tex} \mathrm { MnO } _ { 2 } {/tex}

Explanation

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Q 20. In the standardization of {tex} \mathrm { Na } _ { 2 } \mathrm { S } _ { 2 } \mathrm { O } _ { 3 } {/tex} using {tex} \mathrm { K } _ { 2 } \mathrm { Cr } _ { 2 } \mathrm { O } _ { 7 } {/tex} by iodometry, the equivalent weight of {tex} \mathrm { K } _ { 2 } \mathrm { Cr } _ { 2 } \mathrm { O } _ { 7 } {/tex} is

A

(molecular weight)/2

(molecular weight) /6

C

(molecular weight) / 3

D

same as molecular weight

Explanation

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Q 21. The species that undergoes disproportionation in an alkaline medium are

A

{tex} \mathrm { Cl } _ { 2 } {/tex}

B

{tex} \mathrm { MnO } _ { 4 } ^ { 2 - } {/tex}

C

{tex} \mathrm { NO } _ { 2 } {/tex}

All of these

Explanation

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Q 22. One mole of {tex} \mathrm { N } _ { 2 } \mathrm { H } _ { 4 } {/tex} loses {tex}10{/tex} moles of electrons to form a new compound {tex} Y {/tex}. Assuming that all nitrogen appear in the new compound, what is the oxidation state of nitrogen in {tex} Y {/tex} (There is no change in the oxidation state of hydrogen)

A

{tex} - 1 {/tex}

B

{tex} - 3 {/tex}

{tex} + 3 {/tex}

D

{tex} +5 {/tex}

Explanation

The oxidation state of N in hydrazine is {tex} - 2 {/tex} {tex} 1 {/tex} mole of hydrazine contains {tex} 2 {/tex} moles of N and loses {tex} 10 {/tex} moles of electrons. Hence, {tex} 1 {/tex} N atom will lose {tex} 5 {/tex} electrons. Hence, its oxidation number will increase by {tex} 5 {/tex} Hence, the oxidation number of N in compound of {tex} Y {/tex} will be .

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Q 23. Phosphorus, sulphur and chlorine undergo disproportion in the .. A... medium. Here, A refers to

A

acidic

alkaline

C

neutral

D

Both (a) and (b)

Explanation

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Q 24. In which of the following compounds oxygen has highest oxidation state and in which it has lowest oxidation state? {tex} \mathrm { OF } _ { 2 } , \mathrm { H } _ { 2 } \mathrm { O } _ { 2 } , \mathrm { KO } _ { 2 } , \mathrm { O } _ { 2 } \mathrm { F } _ { 2 } {/tex}

A

Highest {tex} = \mathrm { KO } _ { 2 } , {/tex} lowest {tex} = \mathrm { H } _ { 2 } \mathrm { O } _ { 2 } {/tex}

B

Highest {tex} = \mathrm { OF } _ { 2 } , {/tex} lowest {tex} = \mathrm { H } _ { 2 } \mathrm { O } _ { 2 } {/tex}

Highest {tex} = \mathrm { OF } _ { 2 } , {/tex} lowest {tex} = \mathrm { KO } _ { 2 } {/tex}

D

Highest {tex} = \mathrm { KO } _ { 2 } , {/tex} lowest {tex} = \mathrm { H } _ { 2 } \mathrm { O } _ { 2 } {/tex}

Explanation

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Q 25. The most powerful oxidizing agent from the following is

A

{tex} \mathrm { H } _ { 3 } \mathrm { BO } _ { 3 } {/tex}

B

{tex} \mathrm { HPO } _ { 3 } {/tex}

C

{tex} \mathrm { H } _ { 3 } \mathrm { PO } _ { 4 } {/tex}

{tex} \mathrm { H } _ { 2 } \mathrm { SO } _ { 4 } {/tex}

Explanation