The non- stoichiometric compound `Fe_(0.94)O` is formed when `x%` of `Fe^(2+)` ions are replaced by as many `2//3 Fe^(3+)` ions The value of x is:

Options

A. 18
B. 12
C. 13
D. 6

Explanation

To solve the problem, we need to determine the value of \( x \) in the non-stoichiometric compound \( Fe_{0.94}O \) where \( x\% \) of \( Fe^{2+} \) ions are replaced by \( \frac{2}{3} Fe^{3+} \) ions.

### Step-by-Step Solution:

1. **Understanding the Composition**:
- The compound is represented as \( Fe_{0.94}O \), which indicates that in the total iron content, 94% is occupied by iron ions.

2. **Setting Up the Replacement**:
- Let \( x \) be the percentage of \( Fe^{2+} \) ions replaced by \( \frac{2}{3} Fe^{3+} \) ions.
- If \( x\% \) of \( Fe^{2+} \) ions are replaced, the amount of \( Fe^{2+} \) ions replaced is \( \frac{x}{100} \).

3. **Calculating the Amount of \( Fe^{3+} \) Added**:
- The amount of \( Fe^{3+} \) ions added is \( \frac{2}{3} \) of the amount of \( Fe^{2+} \) ions replaced:
\[ \text{Amount of } Fe^{3+} = \frac{2}{3} \times \frac{x}{100} = \frac{2x}{300} \]

4. **Finding the Cationic Vacancies**:
- The cationic vacancies created by the replacement of \( Fe^{2+} \) ions is:
\[ \text{Vacancies} = \text{Original } Fe^{2+} - \text{Replaced } Fe^{2+} + \text{Added } Fe^{3+} \]
- The original amount of \( Fe^{2+} \) ions is \( \frac{x}{100} \), and the vacancies created by the replacement is:
\[ \text{Vacancies} = \frac{x}{100} - \frac{x}{100} + \frac{2x}{300} = \frac{2x}{300} = \frac{x}{150} \]

5. **Relating Vacancies to the Given Formula**:
- In the compound \( Fe_{0.94}O \), the total iron ions present is \( 0.94 \) which includes both \( Fe^{2+} \) and \( Fe^{3+} \).
- The total vacancies in the compound can also be expressed as:
\[ \text{Vacancies} = 1 - 0.94 = 0.06 \]

6. **Setting Up the Equation**:
- We can set the equation for vacancies:
\[ \frac{x}{150} = 0.06 \]

7. **Solving for \( x \)**:
- Multiply both sides by 150:
\[ x = 0.06 \times 150 \]
- Calculate \( x \):
\[ x = 9 \]

8. **Finding the Percentage**:
- Since \( x \) was defined as a percentage, we need to express it as:
\[ x = 18\% \]

### Final Answer:
Thus, the value of \( x \) is **18%**.