Chemistry by Inam Jazbi: M.C.Qs on Oxidation Number ....Unit # 10

M.C.Qs on Oxidation Number ....Unit # 10

1. Which one is incorrect regarding oxidation?

(a)	It involves addition of oxygen to a substance or removal of hydrogen from a compound.
(b)	It involves the loss of electron and is always accompanied by an increase in oxidation number.
(c)	It always occurs at cathode.
(d)	All of the above.

2. Which one is incorrect regarding reduction?

(a)	It involves addition of hydrogen to a substance or removal of oxygen from oxides.
(b)	It involves the gain of electron and is always accompanied by a decrease in oxidation number.
(c)	It always occurs at anode.
(d)	All of the above.

3. Which one is an example of oxidation reaction?

(a)	Cl	+	e^-	¾¾®	Cl^–
(b)	H₂O			¾¾®	H⁺	+	OH^–
(c)	Ag⁺	+	Cl^–	¾¾®	AgCl
(d)	Al	-	3e^–	¾¾®	Al³⁺

4. Which one is an example of reduction reaction?

(a)	C	+	O₂	¾¾¾¾®	CO₂
(b)	Fe³⁺			¾¾¾¾®	Fe²⁺
(c)	H₂			¾¾¾¾®	2H⁺
(d)	Zn			¾¾¾¾®	Zn²⁺

5. Which one is incorrect regarding oxidizing agent?

(a)	It provides nascent oxygen either on decomposition or on reaction with other substance.
(b)	It acts as electron acceptor.
(c)	It undergoes decrease in oxidation number.
(d)	It always oxidizes itself.

6. Which one is incorrect regarding reducing agent?

(a)	It provides nascent hydrogen either on decomposition or on reaction with other substance.
(b)	It acts as electron donor.
(c)	It undergoes an increase in oxidation number.
(d)	It always reduces itself.

7. Which one of the following reactions involves oxidation and reduction?

(a)	NaBr	+	HCl	¾¾¾¾®	NaCl	+	HBr
(b)	HBr	+	AgNO₃	¾¾¾¾®	AgBr	+	HNO₃
(c)	H₂	+	Br₂	¾¾¾¾®	2HBr
(d)	Na₂O	+	H₂SO₄	¾¾¾¾®	Na₂SO₄	+	2H₂O

8. Which one of the following is not an oxidation-reduction reaction?

(a)	MgO	+	2HCl	¾¾¾¾®	MgCl₂	+	H₂O
(b)	Mg	+	HCl	¾¾¾¾®	MgCl₂	+	H₂
(c)	Cu	+	4HNO₃	¾¾¾¾®	Cu(NO₃)₂	+	2H₂O	+	2NO₂
(d)	Cu	+	2H₂SO₄	¾¾¾¾®	CuSO₄	+	2H₂O	+	SO₂

9. Which one of the following equation does not represent a redox reaction?

(a)	Ba²⁺	+	SO₄²^–	¾¾¾¾®	BaSO₄
(b)	Br₂	+	2I^–	¾¾¾¾®	2Br^–	+	I₂
(c)	Cl₂	+	S^2–	¾¾¾¾®	S	+	2Cl^–
(d)	Cu²⁺	+	Zn	¾¾¾¾®	Cu	+	Zn²⁺

10. Which one is incorrect regarding oxidation number?

(a)	It shows the extent of oxidation or reduction.
(b)	Free elements have zero oxidation number.
(c)	It may have fractional value and it may be zero.
(d)	It is a number without positive or negative sign.

11. When oxidation number of a specie increases in a chemical reaction, the specie is said to be:

(a)	Oxidized	(b)	Reduced
(c)	Electrolyzed	(d)	Hydrolyzed

12. The oxidation number of an element in the free state is always:

(a)	0	(b)	+1
(c)	+2	(d)	-1

13. The oxidation number of oxygen in a molecule is not -2 when it is bonded to a …… atom.

(a)	Ne	(b)	S
(c)	Br	(d)	F

14. The oxidation number of oxygen in OF₂ is:

(a)	+1	(b)	+2
(c)	-2	(d)	-1

15. The oxidation number of oxygen in peroxides (e.g. Na₂O₂, H₂O₂, BaO₂, and SrO₂) is:

(a)	-1	(b)	-1
(c)	- ½	(d)	+2

16. The oxidation number of oxygen in superoxides (e.g. KO₂, RbO₂, and CsO₂) is:

(a)	-1	(b)	-2
(c)	- ½	(d)	+2

17. The oxidation number of hydrogen is +1 in its compounds except in:

(a)	Covalent hydrides	(b)	H₂O
(c)	Ionic hydrides	(d)	CH₄

18. The oxidation number of Pt in K₂PtCl₆ is:

(a)	+2	(b)	+4
(c)	+3	(d)	-4

19. The oxidation number of W in WO₃ is:

(a)	+5	(b)	+2
(c)	+3	(d)	+6

20. The oxidation number of Ni in Ni(CO)₄ is:

(a)	+5	(b)	+4
(c)	Zero	(d)	+3

21. The oxidation number of carbon in C₁₂H₂₂O₁₁ is:

(a)	+12	(b)	-12
(c)	Zero	(d)	+4

22. The oxidation number of chlorine in HClO₄ is:

(a)	+1	(b)	+7
(c)	+5	(d)	+3

23. The oxidation number of S in SO₃^2- is:

(a)	-4	(b)	+4
(c)	-2	(d)	+6

24. The oxidation number of S in S₂O₃^2- is:

(a)	+2	(b)	+4
(c)	-2	(d)	+2.5

25. In which of the following substances does sulphur exhibits is highest oxidation state?

(a)	S₈	(b)	SO₂Cl₂
(c)	Na₂S₄O₆	(d)	Na₂S₂O₃

26. When Cl^– ions are converted to Cl₂, the oxidation number of chlorine increases from:

(a)	-1 to +1	(b)	-1 to zero
(c)	-1 to -2	(d)	-1 to +2

27. The most common oxidation state of an element is -2. The number of electrons present in its outermost shell is:

(a)	4	(b)	6
(c)	5	(d)	2

28. Which one of the following formulae contains nitrogen with an oxidation state of +5?

(a)	NH₄⁺	(b)	N₂O₅
(c)	NO₂	(d)	N₂O

29. The electronic configuration of an element is 1s², 2s² 2p⁵. In a chemical reaction, it is most likely to

(a)	Donate two electrons	(b)	Gain one electron
(c)	Donate one electron	(d)	Gain two electrons

30. An atom has 3 electrons in its valence shell. It is most likely to have following oxidation state?

(a)	-3	(b)	-5
(c)	+2	(d)	+3

31. What is the oxidation number associated of the element with oxygen in each of the following radicals?

(i). CrO₄^2– (ii). ClO₄^1– (iii). PO₄^3– (iv). PbO₂^2–

(a)	+6, +7, +5, +2	(b)	+6, +5, +5, +4
(c)	+2, +5, +7, +6	(d)	+5, +6, +2, +7

32. What is the oxidation number of Mn in the following compounds?

KMnO₄, K₂MnO₄, MnO₂, MnCl₂

(a)	+7, +6, +4, +2	(b)	+7, +2, +6, +4
(c)	+6, +4, +7, +2	(d)	+7, +4, +6, +4

33. What is the oxidation number of Cl in the following compounds?

Cl₂O, HOCl, NaClO₃, AuCl₃, ClF

(a)	+1, +1, +5, -1, -1	(b)	+1, +2, +5, -1, +1
(c)	+1, -1, +3, -1, +1	(d)	+3, +1, +5, -1, -1

34. In which of the following formulae contains Mn in its highest oxidation state?

(a)	MnO₂	(b)	MnO₄¹^–
(c)	MnO₄^2-	(d)	Mn(OH)₃

35. In which of the following formulae contains P in its highest oxidation state?

(a)	P₂O₇²^–	(b)	P₄
(c)	PO₃³^–	(d)	PH₃

36. In which of the following formulae contains C with oxidation state of -2?

(a)	CO	(b)	Al₄C₃
(c)	C₂H₆O	(d)	HCO₃¹^–

37. In which of the following formulae contains C with oxidation state of +4?

(a)	C₆H₁₂O₆	(b)	C₆H₁₀O₅
(c)	CO	(d)	None of them

38. In which of the following formulae contains Cr with oxidation state of +3?

(a)	K₂Cr₂O₇	(b)	H₂CrO₄
(c)	CrO₃	(d)	None of them

39. In which of the following formulae contains O in its highest oxidation state?

(a)	Na₂O	(b)	KO₂
(c)	OF₂	(d)	O₂F₂

40. In the reaction; Zn + H₂SO₄ ¾¾¾¾® ZnSO₄ + H₂, which element is reduced?

(a)	H	(b)	O
(c)	Zn	(d)	S

41. In the reaction; 2HBr + H₂SO₄ ¾¾¾¾® SO₂ + Br₂ + 2H₂O, which element is oxidized?

(a)	S	(b)	Br
(c)	H	(d)	O

42. In the reaction; Zn + I₂ ¾¾¾¾® ZnI₂, which element is oxidized?

(a)	Zinc atom	(b)	Zinc ion
(c)	Iodine atom	(d)	Iodide ion

M.C.Qs on Oxidation Number ....Unit # 10

M.C.Qs on Oxidation Number ....Unit # 10

(a)

(b)

(c)

(d)

(a)

(b)

(c)

(d)

(a)

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(b)

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(c)

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Fe2+

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H2

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(b)

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(c)

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(d)

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H₂O

H⁺

Ag⁺

Cl^–

3e^–

Al³⁺

O₂

CO₂

Fe³⁺

Fe²⁺

H₂

2H⁺

Zn²⁺

AgNO₃

H₂

Br₂

Na₂O

H₂SO₄

Na₂SO₄

MgCl₂