Which of the following is not a method of commercial production of dihydrogen?

Options

A. Electrolysis of acidified water using platinum electrodes gives hydrogen
B. High purity `(gt 99.95%) `dihydrogen is obtained by electrolysis of warm aqueous barium hydroxide solution between the nickel electrodes
C. By electrolysis, it is obtained as a by product in the manufacture of sodium hydroxide and chlorine by the electrolysis of brine solution
D. none of these

Answer

To determine which of the following is not a method of commercial production of dihydrogen, we will analyze each option provided.

### Step-by-Step Solution:

1. **Identify the Options**: We need to evaluate each of the methods listed in the options to see if they are recognized commercial methods for producing dihydrogen.

2. **Evaluate the First Option**:
- **Electrolysis of Acidified Water**: This method involves the electrolysis of water that has been acidified (usually with sulfuric acid) using platinum electrodes.
- **Reaction**:
\[ 2H_2O \rightarrow 2H_2 + O_2 \]
- This method is indeed a commercial method for producing dihydrogen.

3. **Evaluate the Second Option**:
- **Electrolysis of Warm Aqueous Barium Hydroxide**: This method produces high purity dihydrogen (greater than 99.95%) when electrolysis is performed using nickel electrodes.
- This is also recognized as a commercial method for producing dihydrogen.

4. **Evaluate the Third Option**:
- **Electrolysis of Brine Solution**: During the electrolysis of brine (sodium chloride solution), dihydrogen is produced as a byproduct along with chlorine gas and sodium hydroxide.
- **Overall Reaction**:
\[ 2NaCl + 2H_2O \rightarrow Cl_2 + H_2 + 2NaOH \]
- This method is also a recognized commercial method for producing dihydrogen.

5. **Evaluate the Fourth Option**:
- Since the question asks for the option that is NOT a method of commercial production of dihydrogen, we need to identify if any of the above methods are not commercial.
- All three methods discussed (electrolysis of acidified water, electrolysis of barium hydroxide, and electrolysis of brine) are indeed commercial methods.

6. **Conclusion**:
- Since all the mentioned methods are valid commercial production methods for dihydrogen, the correct answer to the question is that none of the options provided are incorrect. Therefore, the answer is **option 4: none of these**.