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Class 9 Electrochemistry MCQs and Answers with explanation

1. In which of the following changes, the nitrogen atom is reduced?





... Answer is b)
Explanation: Oxidation number of an elemnet in free state is zero. So Oxidation No. of N2 = 0
Calculate oxidation No. of nitrogen in each compound.
Option a)
Let, oxidation No. of N in NO is X.
Sum of oxidation numbers of all atoms present in a neutral compound is zero.
Oxidation No. of N + (Oxidation No. of O ) = 0
X-2 = 0
X = +2
X = +2
Oxidation No. of N in NO2 is +2
Option b)
Let, oxidation state of N in NO2 is X.
Sum of oxidation numbers of all atoms present in a neutral compound is zero.
Oxidation No. of N + 2(Oxidation No. of O ) = 0
X + 2(-2) = 0
X -4 = 0
X = +4
Oxidation No. of N in NO2 is +4
Option c)
Let, oxidation state of N in NH3 is X.
Sum of oxidation numbers of all atoms present in a neutral compound is zero.
Oxidation No. of N + 3(Oxidation No. of H ) = 0
X + 3(+1) = 0
X +3 = 0
X = -3
Oxidation No. of N in NH3 is -3
Option d)
Let, oxidation state of N in HNO3 is X.
Sum of oxidation numbers of all atoms present in a neutral compound is zero.
Oxidation No. of H + Oxidation No. of N + 3(Oxidation No. of O ) = 0
1 + X + 3(-2) = 0
1 + X - 6 = 0 = 0
X = +5 = +5
Oxidation No. of N in HNO3 is +5
Correct answer is c as oxidation No. is deceasing only in option c.

2. Which of the following changes reaction is an example of oxidation.





... Answer is b)
Explanation: From siver atom to silver ion, i.e., Ag------>Ag+, oxidation changes from 0 to +1, so it is oxidation. In all other options, oxidation number decreases.
In option a) Cl0-----> Cl-, oxidation decreases from 0 to -1. In option c) O20-----> O2-1, oxidation decreases from 0 to -1. In option d) Fe+3-----> Fe+2, oxidation decreases from +3 to +2.

3. Which of the following elements in the given reaction is reduced?

Reaction of ZnO with hydrogen gas





... Answer is b)
Explanation: From reaction, Zn+2O-2 ---------> Zn0,
So, Zn+2 in ZnO is being reduced. So correct option is b.

4. Consider the following reaction:

Reaction of Hydrogen suphide with Chlorine gas
In this reaction H2S behaves as





... Answer is a)
Explanation: In this reaction, in H2S, S is being oxidized from -2 to 0, so, H2S is a reducing agent while oxidation state of compound Cl2 is being reduced from 0 to -1, so it is acting as oxidizing agent

5. The oxidation state of Cr in K2Cr2O7 is





... Answer is b)
Explanation: Let oxidation No. of Cr in K2Cr2O7 is X.
Sum of oxidation numbers of all atoms present in a neutral compound is zero.
2(Oxidation No. of K) + 2(Oxidation No. of Cr) + 7(Oxidation No. of O) = 0
2(+1) + 2(X) + 7(-2) = 0
2 + 2X- 14 = 0
2X -12 = 0
X = +12/2 = +6
Oxidation No. of Cr in K2Cr2O7 is +6

6. Which of the following statement is not correct about the galvanic cell.





... Answer is c)
Explanation: Electrons flow from anode to cathode in external circut.

7. Which of the following statement is not correct about the Daniel cell





... Answer is a)
Explanation: Half cell of active metal in Daniel cell acts as an anode while less active metal acts as cathode.

8. Which of the following do not involve electrolytic process?





... Answer is d)
Explanation: Reduction of metal oxide by a reducing agent is a chemical process known as smelting. On the other hand, refining of copper, manufacturing of sodium from NaCl and electrochemical process are examples of electrolytic processes.

9. Galvanizing is





... Answer is b)
Explanation: Galvanizing is a process in which clean iron sheet coated is dipped into a hot zinc chloride bath and heated. After this sheet is rolled on zinc bath and cooled.

10. Which of the following is true for the Nelson cell?





... Answer is c)
Explanation: Nelson cell is used for commercial preparation of sodium hydroxide. Chlorine gas is produced at anode by oxidation reaction while hydrogen gas is prouced at cathode by reduction reaction.
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