UP Board Class 11 Chemistry Chapter 7 Redox Reactions Multiple Choice Questions

UP Board Class 11 Chemistry Chapter 7 Redox Reactions Multiple Choice Questions

Question 1. Which of die following substances undergo disproportionation reactions in the basic medium

1. F₂
2. P₄
3. S₂
4. Br₂

Answer: 2,3,4

Question 2. In which of the following compounds, the oxidation number of oxygen is fractional

1. B₄O₁₀
2. B₂H₆
3. CSO₂
4. KO₃

Answer: 1,3,4

Question 3. Wlien Cl₂ is passed through NaOH in the cold, the oxidation number of changes from

1. 0 to -1
2. 0 to +2
3. 0 to -2
4. 0 to -1

Answer: 1,2

Question 4. In which of the following cases equivalent mass of a reductant is equal to its molecular mass

1. \(\mathrm{Cr}_2 \mathrm{O}_7^{2-}+6 \mathrm{I}^{-}+14 \mathrm{H}^{+} \rightarrow 2 \mathrm{Cr}^{3+}+3 \mathrm{I}_2+7 \mathrm{H}_2 \mathrm{O}\)

2. \(\mathrm{MnO}_4^{-}+5 \mathrm{Fe}^{2+}+8 \mathrm{H}^{+} \rightarrow 5 \mathrm{Fe}^{3+}+\mathrm{Mn}^{2+}+4 \mathrm{H}_2 \mathrm{O}\)

3. \(2 \mathrm{Na}_2 \mathrm{~S}_2 \mathrm{O}_3+\mathrm{I}_2 \rightarrow \mathrm{Na}_2 \mathrm{~S}_4 \mathrm{O}_6+2 \mathrm{NaI}\)

4. \(\mathrm{MnO}_4^{-}+5 \mathrm{C}_2 \mathrm{O}_4^{2-}+16 \mathrm{H}^{+} \rightarrow \mathrm{Mn}^{2+}+10 \mathrm{CO}_2+8 \mathrm{H}_2 \mathrm{O}\)

Answer: 2,3

Question 5. Identify the redox reactions

1. 2CuSO₄ + 4KI→2CuI + I₂ + 2K₂SO₄
2. BaCl₂ + Na₂SO₄→BaSO₄ + 2NaGl
3. 3I₂ + 6NaOH→NaIO3 + 5Nal + 3H₂O
4. CuSO₄ + 4NH₃→[Cu(NH₃)₄]SO₄

Answer: 1,3

Question 6. When ammonium nitrate is heated, the oxidation numbers of the N-atoms present it change from

1. -3 to +1
2. -3 to 0
3. -2 to +4
4. +5 to 0

Answer: 2,4

Question 7. For the reaction, \(2 \mathrm{~S}_2 \mathrm{O}_3^{2-}+\mathrm{I}_2 \rightarrow \mathrm{S}_4 \mathrm{O}_6^{2-}+2 \mathrm{I}^{-}-\)

1. \(\mathrm{S}_2 \mathrm{O}_3^{2-} \text { gets oxidised to } \mathrm{S}_4 \mathrm{O}_6^{2-}\)

2. \(\mathrm{S}_2 \mathrm{O}_3^{2-} \text { gets reduced to } \mathrm{S}_4 \mathrm{O}_6^{2-}\)

3. I₂ gets oxidized to I¯

4. I₂ gets reduced to I¯

Answer: 1,4

Question 8. Which of the following statements about the following reaction is wrong

2Cu₂O + Cu₂s→6cu + SO₂

1. Both Cu₂O and cu₂s are reduced
2. Only Cu₂s are reduced
3. Cu₂s is the oxidation
4. Only cu₂O is reduced

Answer: 2,3,4

Question 9. Which of the following orders represents the correct descending order of oxidation numbers

1. HNO₂ > NO > NH₄Cl > N₂
2. HNO₃ > NO > N₂ > NH₂Cl
3. H₂S₂O₇ > Na₂S₂O₃ > Na₂S4O₆ > S₈
4. H₂SO₅ > H₂SO₃ > SCl₂ > H₂S

Answer: 2,4

Question 10. Which ofthe following reactions are not reactions

1. SO₂(g) +H₂O(f) H₂SO₃(aq)

2. Ca(s) + H₂(g) → CaH₂(s)

3. 2H₂S(aq) + SO₂(g)→2H20(l) + 3S(s)

4. \(\begin{aligned}
2 \mathrm{PCl}_5(g)+ & \mathrm{H}_2 \mathrm{SO}_4(a q) \longrightarrow \\
& 2 \mathrm{POCl}_3(a q)+2 \mathrm{HCl}(a q)+\mathrm{SO}_2 \mathrm{Cl}_2(g)
\end{aligned}\)

Answer: 1,4

Question 11. In which compounds do Cr exist +6 oxidation state

1. CrO₂Cl₂
2. Na₂[Cr(CN)₆]
3. CrO₅
4. K₂Cr₂O₇

Answer: 1,3,4

Question 12. When ammonium nitrite (NH₂NO₂) is heated

1. Oxidation of nitrogen takes place
2. Reduction of nitrogen takes place
3. The overall reaction is a disproportionation reaction
4. The overall reaction is a double decomposition reaction

Answer: 1,2,3

Question 13. In which compounds does an atom exist in two different oxidation states

1. H₂SO₅
2. NH₄NO₃
3. Fe₂O₃
4. H₂O₂

Answer: 1,2

Question 14. In the balanced equation for the reaction—

⇒ \(\mathrm{H}_2 \mathrm{SO}_4+x \mathrm{HI} \rightarrow \mathrm{H}_2 \mathrm{~S}+y \mathrm{I}_2+z \mathrm{H}_2 \mathrm{O}\)

1. x=y-z
2. y=z
3. x=2y
4. z=2x

Answer: 2,3

Question 15. In the reaction,

⇒ \(\mathrm{KMnO}_4+\mathrm{Na}_2 \mathrm{~S}_2 \mathrm{O}_3+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{MnO}_2+\mathrm{SO}_4^{2-}+\mathrm{OH}^{-}\)

(Assume formula masses of KMnO₂ and Na₂S₂O₃ M₁ and M₂ respectively)—

1. The equivalent mass of KMnO₂ = M₁/3
2. The equivalent mass of Na₂S₂O₃ = M₂
3. The equivalent mass of KMnO₄ = M₁/5
4. The equivalent mass of Na₂S₂O₂ = M₂/8

Answer: 1,4

Question 16. In the balanced equation for the reaction,

⇒ \(\mathrm{UO}^{2+}+\mathrm{Cr}_2 \mathrm{O}_7^{2-}+\mathrm{H}^{+} \rightarrow \mathrm{UO}_2^{2+}+\mathrm{Cr}^{3+}+\mathrm{H}_2 \mathrm{O}\) the coefficient of-

1. UO²⁺
2. \(\mathrm{UO}_2^{2+} \text { is } 3\)
3. \(\mathrm{Cr}_2 \mathrm{O}_7^{2-} \text { is } 1\)
4. H₂O is 7

Answer: 2,3,4

Question 17. The disproportionation of 1 mol of \(\mathrm{MnO}_4^{2-}\) ions in a neutral aqueous solution results in

1. 1/3 mol of MnO¯₄
2. 2/3 mol of MnO₂
3. 2/3 mol of MnO₄
4. 1/3 mol of MnO₂

Answer: 3,4

Question 18. In the reaction the oxidation number of marked with (*)-

1. Increases by 2 units
2. Increases by 1 unit
3. Decreases by 2 units
4. Decreases by 3 units

Answer: 1,3

Question 19. For the reaction: SO₂ + 2H₂S→3S + 2H₂O 

1. The equivalent mass of the oxidant is 64
2. Equivalent mass ofoxidantis 16
3. The number of electrons accepted oxidant is 4
4. The number of electrons lost by reductant is 6

Answer: 2,3

Question 20. The species that cannot be reducing agents are

1. SO₃
2. \(\mathrm{SO}_3^{2-}\)
3. H₂SO₄
4. S^2-

Answer: 1,3

Question 21. Which are conserved all redox reactions

1. Charge
2. Mass
3. Either charger or Mass
4. Neither charge nor mass

Answer: 1,2

Question 22. The equivalent weight of K₂Cr₂O₇ in an acidic medium is expressed in terms of its molecular weight (M) as

1. \(\frac{M}{3}\)
2. \(\frac{M}{4}\)
3. \(\frac{M}{6}\)
4. \(\frac{M}{7}\)

Answer: 3. \(\frac{M}{6}\)

In an acidic medium, K₂Cr₂O₇ undergoes reduction, forming a Cr³⁺ ion.

⇒ \(\mathrm{Cr}_2 \mathrm{O}_7^{2-}+14 \mathrm{H}^{+}+6 e \rightarrow 2 \mathrm{Cr}^{3+}+7 \mathrm{H}_2 \mathrm{O}\)

In this reaction, the equivalent weight of K₂Cr₂O₇

⇒ \(=\frac{\text { Molecular weight of } \mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7}{\begin{array}{c}
\text { No of electrons gained by a molecule of } \mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7 \\
\text { in its reduction }
\end{array}}=\frac{M}{6}\)

Question 23. If Cl₂ is passed through hot aqueous NaOH, the products formed have Cl in different oxidation states. These are indicated as

1. -1 and +1
2. -1 and +5
3. -1 and +5
4. -1 and +3

Answer: 2. -1 and +5

Reaction: Cl₂ + 6NaOH→NaCl + 5NaC1O₃ + 3H₂O The oxidation number of Cl in NaCl is -1 and that in NaCIO₃ is +5.

Question 24. In an aqueous alkaline solution, two-electron reductions of HO‾₂ give—

1. HO‾
2. H₂O
3. O₂
4. O‾₂

Answer: 1. HO‾

Question 25. Consider the following reactions

⇒ \(x \mathrm{MnO}_4^{-}+y \mathrm{C}_2 \mathrm{O}_4^{2-}+z \mathrm{H}^{+} \rightarrow x \mathrm{Mn}^{2+}+2 y \mathrm{CO}_2+\frac{z}{2} \mathrm{H}_2 \mathrm{O}\)

The values of x, y, and z in the reaction are respectively

1. 5,2 And 8
2. 5,2 and 16
3. 2,5 and 8
4. 2,5 and 16

Answer: 4. 2,5 and 16

⇒ \({\left[\mathrm{MnO}_4^{-}+8 \mathrm{H}^{+}+5 e \rightarrow \mathrm{Mn}^{2+}+4 \mathrm{H}_2 \mathrm{O}\right] \times 2}\)

⇒ \(\frac{\left[\mathrm{C}_2 \mathrm{O}_4^{2-} \rightarrow 2 \mathrm{CO}_2+2 e\right] \times 5}{2 \mathrm{MnO}_4^{-}+5 \mathrm{C}_2 \mathrm{O}_4^{2-}+16 \mathrm{H}^{+} \rightarrow 2 \mathrm{Mn}^{2+}+10 \mathrm{CO}_2+8 \mathrm{H}_2 \mathrm{O}}\)

‍∴ x=2, y=5 and z=16

Question 26. In which of the following reactions, H₂O₂ acts as a reducing agent-

1. H₂O₂ + 2H+ + 2e→2H₂O
2. H₂O₂-2e→ O₂ + 2H⁺
3. H₂O₂ + 2e→2OH¯
4. H₂O₂ + 2OH¯-2e→O₂ + 2H₂O

Choose the correct option 

1. 2,4
2. 1,2
3. 3,4
4. 1,3

Answer: 1. 2,4

In the reaction, H₂O₂ → O₂ + 2H+ + 2e, electrons are lost by H₂O₂ and hence H₂O₂ acts as a reductant. In the reaction, H₂O₂+2OH¯→ O₂ + 2H₂O + 2e, electrons are lost by H₂O₂ and hence H₂O₂ acts as a reductant.

Question 27. The Pair in which phosphorus atoms have a formal oxidation state of +3 is-

1. Orthophosphoric and Pyrophosphoric acid
2. Pyrophosphorus and Hypophosphoric acid
3. Orthophosphoric and Hypophosphoric acid
4. Pyrophosphorus and Pyrophosphoric acid

Answer: 1. Orthophosphorus and pyrophosphoric acid

Orthophosphoric acid: \(\begin{aligned}
& +1+3-2 \\
& \mathrm{H}_3 \mathrm{PO}_3
\end{aligned}\)

Pyrophosphorus acid:

Let the oxidation number of P in pyrophosphoric acid be x.

So, 4(+1) + 2x + 5(-2) = 0

or, 2x = 6 or, x = +3

Question 28. Which of the following reactions is an example of a redox creation:

1. XeFG + H₂O→XeOF4 + 2HF
2. XeF₆ + 2H₂O→XeO₂F₂ + 4HF
3. XeF₄ +O₂F₄→XeF₆ + O₂
4. XeF₂ + PF₅→[XeF]+[PF₆]-

Answer: 3. XeF₄ + O₂F₄→XeF₆ + O₂

⇒ \(\stackrel{+6-1}{\mathrm{XeF}_6}+\mathrm{H}_2 \stackrel{-2}{\mathrm{O}} \rightarrow \mathrm{XeOF}_4^{-2-1}+2 \mathrm{HF}\)

⇒ \(\stackrel{+6}{\mathrm{XeF}_6-1}+2 \mathrm{H}_2 \stackrel{-2}{\mathrm{O}} \xrightarrow[\rightarrow]{+6} \mathrm{XeO}_2^{-2-1} \mathrm{~F}_2+4 \mathrm{HF}\)

⇒ \(\stackrel{+2}{\mathrm{XeF}_2^{-1}}+\stackrel{+5-1}{\mathrm{PF}_2^{-1}} \rightarrow\left[\stackrel{+2}{\mathrm{XeF}} \mathrm{F}^{-1}\right]\left[\mathrm{PF}_6^{-1}\right]\)

For these reactions, there is no change in the oxidation number of the respective elements. So these reactions are not redox reactions.

⇒ \(\stackrel{+4}{\mathrm{XeF}_4}+\stackrel{+4}{\mathrm{O}_2} \mathrm{~F}_4^{-1} \rightarrow \stackrel{+6}{\mathrm{X}} \mathrm{XeF}_6-\stackrel{0}{\mathrm{O}}_2\)

Question 29. The oxidation states of Cr in [Cr(H₂O) ]Cl₃ [Cr(C₆HG)₂] and K2[Cr(CN₂)(0)₂(O₂)(NH₃)] respectively are

1. +3,+4 and +6
2. +3,+2 and +4
3. +3,0 and +6
4. +3,0 and +4

Answer: 3. +3,0 and +6

⇒ \(\left[\stackrel{+3}{\mathrm{Cr}}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right] \mathrm{Cl}_3,\left[\stackrel{0}{\mathrm{Cr}}\left(\mathrm{C}_6 \mathrm{H}_6\right)_2\right]\)

In K₂[Cr(CN)₂(O₂)(0)₂(NH₃)] compound, let, the oxidation number of Cr be x.

or, 2 + X-2-4-2 + 0

or, x = +6

Question 30. A mixture of potassium, Oxalic acid, and sulphuric acid is heated. During the reaction which element undergoes maximum change in the oxidation number-

1. S
2. H
3. Cl
4. C

Answer: 3. Cl

Question 31. In which of the following compounds, nitrogen exhibits the highest oxidation state—

1. N₂H₄
2. NH₃
3. N₃H
4. NH₂OH

Answer: 3. N₃H

⇒ \(\stackrel{-2}{\mathrm{~N}_2} \mathrm{H}_4, \stackrel{-3}{\mathrm{~N}} \mathrm{H}_3, \stackrel{-1 / 3}{\mathrm{~N}} \mathrm{H}_3 \mathrm{H}, \stackrel{-1}{\mathrm{~N}} \mathrm{H}_2 \mathrm{OH}\)

Question 32. In acidic medium, H₂O₂ changes \(\mathrm{Cr}_2 \mathrm{O}_7^{2-}\) to CrO₅ which has two (—0—0— ) bonds. The oxidation state of Cr in CrO₅ is-

1. +5
2. +3
3. +6
4. -10

Answer: 3. +6 let the oxidation number of Cr in CrO₅ be x

Question 33.

1. H₂O₂ + O₃ →H₂O + 2O₂
2. H₂O₂ + Ag₂O→ 2Ag + H₂O + O₂

The role of hydrogen peroxide in the above reactions is respectively—

1. Oxidisingin (1) and reducing (2)
2. Reducing (1) and oxidising (2)
3. Reducing (1) and (12)
4. Oxidisingin (1) and (2)

Answer: 3. Reducing (1) and (12)

⇒ \(\mathrm{H}_2 \stackrel{-1}{\mathrm{O}}_2+\stackrel{0}{\mathrm{O}}_3 \rightarrow \mathrm{H}_2 \mathrm{O}+2 \stackrel{0}{\mathrm{O}}_2\)

In this reaction, H₂O₂ undergoes oxidation and forms O₂. Hence, it acts as a reductant

Question 34. Assuming complete ionization, the same moles of which of the following compounds will require the least amount of acidified KMnO₄ for complete oxidation—

1. FeSO₄
2. FeSO₃
3. FeC₂O₄
4. Fe(NO₂)₂

Answer: 1. FeSO₄ will require the least amount of acidified KMnO₄ for complete oxidation.

Question 35. Hot concentrated sulphuric acid is a moderately strong oxidizing agent. Which of the following reactions does not show oxidizing behavior-

1. Cu + 2H₂SO₄→CuSO₄ + SO₂ + 2H₂O
2. S + 2H₂SO₄→3SO₂ + 2H₂O
3. C + 2H₂SO₄→CO₂ + 2SO₂ + 2H₂O
4. CaF₂ + H₂SO₄→CaSO₄ + 2HF

Answer: 4. CaF₂ + H₂SO₄→CaSO₄ + 2HF

In this reaction, there is no change in the oxidation number of any elements, present. Thus, it is not a redox reaction.

Question 76. For the redox reaction

⇒ \(\mathrm{MnO}_4^{-}+\mathrm{C}_2 \mathrm{O}_4^{2-}+\mathrm{H}^{+} \rightarrow \mathrm{Mn}^{2+}+\mathrm{CO}_2+\mathrm{H}_2 \mathrm{O}\)

The correct coefficients of the reactants for the balanced equation are:

1. 16,5,2
2. 2,5,16
3. 2,16,5
4. 5,16,2

Answer: 2. 2,5,16

⇒ \({\left[\mathrm{MnO}_4^{-}+8 \mathrm{H}^{+}+5 e \rightarrow \mathrm{Mn}^{2+}+4 \mathrm{H}_2 \mathrm{O}\right] \times 2}\)

⇒ \({\left[\mathrm{C}_2 \mathrm{O}_4^{2-} \rightarrow 2 \mathrm{CO}_2+2 e\right] \times 5}\)

⇒ \(2 \mathrm{MnO}_4^{-}+5 \mathrm{C}_2 \mathrm{O}_4^{2-}+16 \mathrm{H}^{+} \rightarrow \mathrm{Mn}^{2+}+10 \mathrm{CO}_2+8 \mathrm{H}_2 \mathrm{O}\)

Question 77. When KMnO₄ reacts with KBr in an alkaline medium and gives a bromate ion, the oxidation state of Mn changes from +7 to

1. +6
2. +4
3. +3
4. +2

Answer: 2. +4

⇒ \(2 \mathrm{MnO}_4^{-}+\mathrm{Br}^{-}+\mathrm{H}_2 \mathrm{O} \rightarrow 2 \stackrel{+4}{2} \mathrm{MnO}_2+\mathrm{BrO}_3^{-}+2 \mathrm{OH}^{-}\)

Question 38. K₂Cr₂O₇ in an acidic medium converts into

1. Cr²⁺
2. Cr²⁺
3. Cr⁴⁺
4. Cr⁵⁺

Answer: 2. Cr²⁺

Question 39. The oxidation state of iron in hemoglobin is

1. 0
2. +2
3. -2
4. +3

Answer: 2. +2

Question 40. What is the oxidation number of Br in KBrO₂

1. +6
2. +7
3. +5
4. +8

Answer: 2. +7

Question 41. Substances that are oxidized and reduced in the following reaction are respectively—

⇒ \(\mathrm{N}_2 \mathrm{H}_4(l)+2 \mathrm{H}_2 \mathrm{O}_2(l) \rightarrow \mathrm{N}_2(g)+4 \mathrm{H}_2 \mathrm{O}(l)\)

1. N₂H₄H₂O
2. N₂H₄H₂O₂
3. N₂H₂O₂
4. H₂O₂N₂

Answer: 2. N₂H₄H₂O₂