Oxidation Number - Class 11 Chemistry MCQ

This set of Class 11 Chemistry Chapter 8 Multiple Choice Questions & Answers (MCQs) focuses on “Redox Reactions – Oxidation Number”.

1. Can 1/2 be an oxidation number?
a) yes
b) no
c) may be
d) cannot say
View Answer

Answer: a
Explanation: The oxidation number is defined as the change in which appears to have when all other atoms are removed from it as ions it can be a whole number or a fractional or 0. So 1/2 can be an oxidation number.

2. The oxidation number of oxygen in Ozone is 1, -1 and 0.
a) true
b) false
View Answer

Answer: a
Explanation: An element may have different values of oxidation number depending upon the nature of the compound in which it is present. Ozone molecule has three oxygens and the oxidation numbers of them are 1, – 1 and 0.

3. Helium element has an Oxidation state of ____________
a) 2
b) 0
c) 1
d) -1
View Answer

Answer: b
Explanation: All elements in the elementary state have an oxidation number of zero. So helium element also has an Oxidation state of zero. It is one of the most important points for determining the oxidation number.

4. In NaH, the oxidation state of hydrogen is _______________
a) 2
b) 1
c) -1
d) 0
View Answer

Answer: c
Explanation: In all compounds except ionic metal hydride the oxidation number of hydrogen is +1. But in metal hydrides like sodium hydride, magnesium hydride, calcium hydride, etc, the oxidation number of hydrogen as -1.

5. What is the oxidation state of Cr in CrO₅?
a) 3
b) 4
c) 5
d) 6
View Answer

Answer: d
Explanation: The oxidation states of oxygens in CrO₅ are -1, -1, -1, -1 and -2. The oxidation state of Cr is given by x. Therefore x + 4(-1) + (-2)(1) = 0. X = 6. The oxidation state of chromium in chromium peroxide is 6.

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6. What is the oxidation state of C in C₃O₂?
a) 0
b) 2
c) -2
d) 0, 2, 2
View Answer

Answer: d
Explanation: The structure of C₃O₂ is given as O=C=C=C=O. Where the oxidation number of carbon beside oxygen is +2 due to oxygen’s -2 oxidation state. And the middle carbon’s oxidation is 0, due to +2 charge on it’s both sides.

7. What is the oxidation state of N in NH₄NO₃ (in order)?
a) -3, 5
b) 5, -3
c) 5
d) -3
View Answer

Answer: a
Explanation: Dividing into two parts oxidation number of N in NH₄⁺ is x; x + 4*1 = +1; x = -3, oxidation number of N in NO₃^– is y; y + 3*-2 = -1; y = 5. The oxidation States of Nitrogen in this compound are -3 and 5 respectively.

8. What is the average oxidation state of S in Na₂S₆O₆?
a) 5
b) 0
c) 5/2
d) 2
View Answer

Answer: c
Explanation: the average Oxidation state of elements in a compound is the average of the different oxidation States. The average oxidation state of S in Na₂S₆O₆ is x. 2(1) + 4x + 6(-2) = 0; x = 5/2. The average Oxidation state of sulfur here is 5/2.

9. What is the stock notation of cuprous oxide?
a) copper oxide
b) copper (I) oxide
c) copper 1 oxide
d) copper 2 oxide
View Answer

Answer: b
Explanation: The elements exhibiting different Oxidation States i.e. are denoted by Roman numeral such as I, II, III, IV etc, within parenthesis after the symbol or name of the element this is known as stock notation.

10. What is the stock notation of mercuric chloride?
a) Mercury
b) Mercuric chloride
c) Chloride
d) Mercury (II) chloride
View Answer

Answer: d
Explanation: The system that exhibits variable oxidation States in specified Roman numerals within parentheses after the symbol is the name of the element is known as stock notation. Mercury (II) chloride is in stock notation.

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