Choose the option with correct words to fill in the blanks.
According to preferential discharge theory, out of number of ions the one which requires ____ energy will be liberted ____ at a given electrode.

Options

A. least, first
B. least, last
C. highest, first
D. highest, last

Answer

To solve the question, we need to fill in the blanks based on the preferential discharge theory in electrochemistry. Let's break it down step by step.

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks us to fill in the blanks in a statement regarding the preferential discharge theory, which relates to the discharge of ions during electrolysis.

2. **Recalling the Preferential Discharge Theory**: According to this theory, when an electrolytic solution contains multiple ions, not all ions are discharged at the electrodes at the same time. Instead, certain ions are preferentially discharged based on their energy requirements.

3. **Identifying Key Concepts**:
- The ion that requires the least energy is discharged first.
- This means that the energy requirement is inversely related to the likelihood of discharge.

4. **Filling in the Blanks**:
- The first blank should be filled with "least" because the ion that requires the least energy will be discharged first.
- The second blank should be filled with "first" to indicate the order of discharge.

5. **Final Statement**: According to preferential discharge theory, out of a number of ions, the one which requires **least** energy will be liberated **first** at a given electrode.

### Answer:
According to preferential discharge theory, out of a number of ions, the one which requires **least** energy will be liberated **first** at a given electrode.