Which of the following is not an application of electrochemical series?

Options

A. To compare the relative oxidising and reducing power of substances.
B. To predict evolution of hydrogen gas on reaction of metal with acid.
C. To predict spontaneity of a redox reaction.
D. To calculate the amount of metal deposited on cathode.

Explanation

To solve the question of which option is not an application of the electrochemical series, we will analyze each option one by one.

### Step 1: Understand the Electrochemical Series
The electrochemical series is a list of standard electrode potentials of various half-reactions. It helps in predicting the behavior of different substances in electrochemical reactions, including their oxidizing and reducing abilities.

### Step 2: Analyze Each Option
- **Option A: To compare the relative oxidizing and reducing power of substances.**
- This is indeed an application of the electrochemical series. The series allows us to see which substances can act as oxidizers or reducers based on their standard electrode potentials.

- **Option B: To predict the evolution of hydrogen gas on reaction of metal with acid.**
- This is also an application of the electrochemical series. By comparing the electrode potentials, we can determine whether a metal will displace hydrogen from an acid, leading to the evolution of hydrogen gas.

- **Option C: To predict the spontaneity of a redox reaction.**
- This is another application of the electrochemical series. The series helps in determining whether a redox reaction will occur spontaneously by comparing the standard electrode potentials of the reactants.

- **Option D: To calculate the amount of metal deposited on the cathode.**
- This is not an application of the electrochemical series. The amount of metal deposited on the cathode during electrolysis is calculated using Faraday's laws of electrolysis, not directly from the electrochemical series.

### Step 3: Conclusion
Based on the analysis, the correct answer is **Option D**, as it does not relate to the applications of the electrochemical series.

### Final Answer
**Option D: To calculate the amount of metal deposited on cathode.**

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