Redox Reactions Questions — NEET Chemistry

Q1

Consider the following compounds :

{\mathrm{\underline{K}O}}_2, \mathrm{H}_2 \underline{\mathrm{O}}_2

and

\mathrm{H}_2 \underline{S }O_4

The oxidation state of the underlined elements in them are, respectively,

A

+1,-2

, and +4

B

+4,-4

, and +6

C

+1,-1

, and +6

D

+2,-2

, and +6

Correct Answer

Option C

Solution

$\mathrm{KO}_2 \rightarrow$ Alkali metal always shows +1 oxidation state.

Therefore oxidation state of K is +1 .

Oxidation state of oxygen in $\mathrm{H}_2 \mathrm{O}_2$ is -1 Oxidation state of sulphur in $\mathrm{H}_2 \mathrm{SO}_4$ is +6 .

Q2

Which reaction is NOT a redox reaction?

A

\mathrm{Zn}+\mathrm{CuSO}_4 \rightarrow \mathrm{ZnSO}_4+\mathrm{Cu}

B

2 \mathrm{KClO}_3+\mathrm{I}_2 \rightarrow 2 \mathrm{KIO}_3+\mathrm{Cl}_2

C

\mathrm{H}_2+\mathrm{Cl}_2 \rightarrow 2 \mathrm{HCl}

D

\mathrm{BaCl}_2+\mathrm{Na}_2 \mathrm{SO}_4 \rightarrow \mathrm{BaSO}_4+2 \mathrm{NaCl}

Correct Answer

Option D

Solution

This is not a redox reaction as there is no change in oxidation state.

Q3

The correct option for a redox couple is:

A Both are oxidised forms involving same element.

B Both are reduced forms involving same element.

C Both the reduced and oxidised forms involve same element.

D Cathode and anode together.

Correct Answer

Option C

Solution

Redox couple is both the reduced and oxidised form involve same element.

Q4

On balancing the given redox reaction,

\mathrm{aCr}_{2} \mathrm{O}_{7}^{2-}+\mathrm{bSO}_{3}^{2-}(\mathrm{aq})+\mathrm{cH}^{+}(\mathrm{aq}) \rightarrow 2 \mathrm{aCr}^{3+}(\mathrm{aq})+\mathrm{bSO}_{4}^{2-}(\mathrm{aq})+\dfrac{\mathrm{c}}{2} \mathrm{H}_{2} \mathrm{O}(\ell)

the coefficients

\mathrm{a}, \mathrm{b}

and

\mathrm{c}

are found to be, respectively -

A 3, 8, 1

B 1, 8, 3

C 8, 1, 3

D 1, 3, 8

Correct Answer

Option D

Solution

Reaction has to be balanced in acidic medium 'O' atoms are balanced by adding

\mathrm{H}_{2} \mathrm{O}

and then

\mathrm{H}

-atom is balanced by adding

\mathrm{H}^{+}

ions and charge is balanced by

e^{\ominus}

. Oxidation:

\left.\mathrm{SO}_{3}^{2-}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{SO}_{4}^{2-}+2 \mathrm{H}^{+}+2 e^{\ominus}\right] \times 3

Reduction:

\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+14 \mathrm{H}^{+}+6 e^{\ominus} \rightarrow 2 \mathrm{Cr}^{3+}+7 \mathrm{H}_{2} \mathrm{O}

\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+3 \mathrm{SO}_{3}^{2-}+8 \mathrm{H}^{\oplus} \rightarrow 2 \mathrm{Cr}^{3+}+3 \mathrm{SO}_{4}^{2-}+4 \mathrm{H}_{2} \mathrm{O}

\mathrm{a}=1

\mathrm{b}=3

\mathrm{c}=8

Q5

Which of the following reactions is a decomposition redox reaction?

A P 4 (s) + 3OH

-

(aq) + 3H 2 O(l)

\to

PH 3 (g) + 3H 2 PO

_2^ -

(aq)

B 2Pb(NO 3 ) 2 (s)

\to

2PbO(s) + 4NO 2 (g) + O 2 (g)

C N 2 (g) + O 2 (g)

\to

2NO(g)

D Cl 2 (g) + 2OH

-

(aq)

\to

ClO

-

(aq) + Cl

-

(aq) + 4H 2 O(l)

Correct Answer

Option B

Solution

Decomposition redox reaction leads to breakdown of a compound into two or more compounds at least one of which must be in the elemental state with change in oxidation number.

\mathrm{2Pb{\left( {N\mathop {{O_3}}\limits^{2 - } } \right)_2}(s) \to 2PbO(s) + 4N{O_2}(g) + \mathop {{O_2}}\limits^0 (g)}

Q6

What is the change in oxidation number of carbon in the following reaction? CH 4 (g) + 4Cl 2 (g)

\to

CCl 4 (l) + 4HCl(g)

A 0 to + 4

B

-

4 to + 4

C 0 to

-

4

D + 4 to + 4

Correct Answer

Option B

Solution

Change in oxidation state of carbon is from $-$ 4 to + 4

Q7

Which of the following reactions are disproportionation reaction? (a) 2Cu +

\to

Cu 2+ + Cu 0 (b) 3MnO 4 2- + 4H +

\to

2MnO 4 - + MnO 2 + 2H 2 O (c) 2KMnO 4

\overset{\Delta}\longrightarrow

K 2 MnO 4 + MnO 2 + O 2 (d) 2MnO 4 - + 3Mn 2+ + 2H 2 O

\to

5MnO 2 + 4

{H^ \oplus }

Select the correct option from the following :

A (a), (c) and (d)

B (a) and (b) only

C (a) and (d) only

D (a), (b) and (c)

Correct Answer

Option B

Solution

In a disproportionation reaction, same substance undergoes oxidation (increase in oxidation number) and reduction (decrease in oxidation number forming two different products.

Q8

The correct order of N-compounds in its decreasing order of oxidation states is

A HNO 3 , NO, N 2 , NH 4 Cl

B HNO 3 , NO, NH 4 Cl, N 2

C HNO 3 , NH 4 Cl, NO, N

D NH 4 Cl, N 2 , NO, HNO 3

Correct Answer

Option A

Solution

H\mathop N\limits^{ + 5} {O_3},\mathop N\limits^{ + 2} O,\mathop {{N_2}}\limits^0 ,\mathop N\limits^{ - 3} {H_4}Cl

Q9

For the redox reaction, MnO 4 – + C 2 O 4 2– + H +

\to

Mn 2+ + CO 2 + H 2 O The correct coefficients of the reactants for the balanced equation are

A <table class=tg> <thead> <tr> <th class=tg-baqh>MnO<sub>4</sub><sup>-</sup></th> <th class=tg-baqh>C<sub>2</sub>O<sub>4</sub><sup>2-</sup></th> <th class=tg-baqh>H<sup>+</sup></th> </tr> </thead> <tbody> <tr> <td class=tg-baqh>16</td> <td class=tg-baqh>5</td> <td class=tg-baqh>2</td> </tr> </tbody> </table>

B <table class=tg> <thead> <tr> <th class=tg-baqh>MnO<sub>4</sub><sup>-</sup></th> <th class=tg-baqh>C<sub>2</sub>O<sub>4</sub><sup>2-</sup></th> <th class=tg-baqh>H<sup>+</sup></th> </tr> </thead> <tbody> <tr> <td class=tg-baqh>2</td> <td class=tg-baqh>5</td> <td class=tg-baqh>16</td> </tr> </tbody> </table>

C <table class=tg> <thead> <tr> <th class=tg-baqh>MnO<sub>4</sub><sup>-</sup></th> <th class=tg-baqh>C<sub>2</sub>O<sub>4</sub><sup>2-</sup></th> <th class=tg-baqh>H<sup>+</sup></th> </tr> </thead> <tbody> <tr> <td class=tg-baqh>2</td> <td class=tg-baqh>16</td> <td class=tg-baqh>5</td> </tr> </tbody> </table>

D <table class=tg> <thead> <tr> <th class=tg-baqh>MnO<sub>4</sub><sup>-</sup></th> <th class=tg-baqh>C<sub>2</sub>O<sub>4</sub><sup>2-</sup></th> <th class=tg-baqh>H<sup>+</sup></th> </tr> </thead> <tbody> <tr> <td class=tg-baqh>5</td> <td class=tg-baqh>16</td> <td class=tg-baqh>2</td> </tr> </tbody> </table>

Correct Answer

Option B

Solution

The correct balanced equation is 2MnO 4 – + 5C 2 O 4 2– + 16H + $\to$ 2Mn 2+ + 10CO 2 + 8H 2 O

Q10

Hot concentrated sulphate acid is a moderately strong oxidizing agent. Which of the following reactions does not show oxidizing behaviour?

A Cu + 2H 2 SO 4

\to

CuSO 4 + SO 2 + 2H 2 O

B S + 2H 2 SO 4

\to

3SO 2 + 2H 2 O

C C + 2H 2 SO 4

\to

CO 2 + 2SO 2 + 2H 2 O

D CaF 2 + H 2 SO 4

\to

CaSO 4 + 2HF

Correct Answer

Option D

Solution

CaF 2 + H 2 SO 4 $\to$ CaSO 4 + 2HF Here, the oxidation state of every atom remains the same so, it is not a redox reaction.