Last traces of water is removed is removed from `H_(2)O_(2)` by

Options

A. electrolysis
B. crystallisation
C. condensation
D. evaporation.

Answer

To solve the question of how the last traces of water are removed from hydrogen peroxide (H₂O₂), we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Problem**: We need to remove the last traces of water from hydrogen peroxide (H₂O₂). Hydrogen peroxide is a liquid that can contain water as an impurity.

2. **Cooling Method**: The problem suggests using a cooling method. A 90% solution of hydrogen peroxide is cooled using a solid carbon dioxide (CO₂) and ether bath. This method is effective because it lowers the temperature significantly, which can help in the crystallization process.

3. **Crystallization**: As the solution is cooled, the hydrogen peroxide will begin to crystallize. Crystallization is a process where a solute (in this case, H₂O₂) forms a solid crystal from a solution. This process helps in separating the pure hydrogen peroxide from the water.

4. **Separation of Crystals**: Once crystallization sets in, the crystals of hydrogen peroxide can be separated from the remaining liquid. This is typically done through filtration or decantation.

5. **Melting and Refreezing**: After separating the crystals, they are melted and then refrozen. This step is repeated to further concentrate the hydrogen peroxide and remove any remaining water.

6. **Final Result**: After several cycles of crystallization, melting, and refreezing, the last traces of water are effectively removed from the hydrogen peroxide.

### Conclusion:
The last traces of water are removed from H₂O₂ by the process of **crystallization**.