Tourmalene is a class of cyclosilicates with general formula.
`(Ca, K, Na) (Al, Fe, Li, Mg, Mn)_(3)(Al, Cr, Fe, V)_(6) (BO_(3))_(3) (Si, Al, B)_(6)O_(18)(OH, F)_(4)`
Which of the following is not a correct example of tourmalene ?

Options

A. `CaAl_(3)Fe_(6)(BO_(3))_(3)S_(6)O_(18)F_(4)`
B. `Ca_(2)Li_(3)V_(6)(BO_(3))_(3)Si_(6)O_(18)(OH)_(4)`
C. `KMg_(3)Cr_(6)(BO_(3))_(3)Si_(6)O_(18)F_(4)`
D. `CaAl_(9)(BO_(3)_(3)Si_(6)O_(18)(OH)_(4)`

Explanation

To determine which of the given compounds is not a correct example of tourmaline, we need to calculate the sum of the oxidation states (charges) for each compound and check if they equal zero. A correct example of tourmaline should be a neutral compound, meaning the total charge should sum to zero.

### Step-by-Step Solution:

1. **Identify the Charges of Each Element**:
- Calcium (Ca) has a charge of +2.
- Aluminium (Al) has a charge of +3.
- Iron (Fe) can have a charge of +2 or +3; we will check both cases.
- Boron (B) in the form of BO3 has a charge of -3.
- Silicon (Si) has a charge of +4.
- Oxygen (O) has a charge of -2.
- Hydroxide (OH) has a charge of -1.

2. **Write the General Formula**:
The general formula for tourmaline is:
\[ (Ca, K, Na) (Al, Fe, Li, Mg, Mn)_{3} (Al, Cr, Fe, V)_{6} (BO_{3})_{3} (Si, Al, B)_{6}O_{18}(OH, F)_{4} \]

3. **Calculate the Total Charge for Each Compound**:
Let's denote the compounds as A, B, C, and D for simplicity. We will calculate the charges for each one.

- **Compound A**:
\[ \text{Charge} = (1 \times +2) + (3 \times +3) + (6 \times +2 \text{ or } +3) + (3 \times -3) + (6 \times +4) + (18 \times -2) + (4 \times -1) \]
- If Fe = +2:
\[ = 2 + 9 + 12 - 9 + 24 - 36 - 4 = -2 \quad (\text{not zero}) \]
- If Fe = +3:
\[ = 2 + 9 + 18 - 9 + 24 - 36 - 4 = -2 \quad (\text{not zero}) \]

- **Compound B**:
\[ \text{Charge} = (1 \times +1) + (3 \times +3) + (6 \times +2) + (3 \times -3) + (6 \times +4) + (18 \times -2) + (4 \times -1) \]
\[ = 1 + 9 + 12 - 9 + 24 - 36 - 4 = -3 \quad (\text{not zero}) \]

- **Compound C**:
\[ \text{Charge} = (1 \times +1) + (3 \times +3) + (6 \times +3) + (3 \times -3) + (6 \times +4) + (18 \times -2) + (4 \times -1) \]
\[ = 1 + 9 + 18 - 9 + 24 - 36 - 4 = 0 \quad (\text{zero}) \]

- **Compound D**:
\[ \text{Charge} = (1 \times +1) + (3 \times +3) + (6 \times +2) + (3 \times -3) + (6 \times +4) + (18 \times -2) + (4 \times -1) \]
\[ = 1 + 9 + 12 - 9 + 24 - 36 - 4 = -3 \quad (\text{not zero}) \]

4. **Conclusion**:
Based on the calculations, Compound A, B, and D do not sum to zero, while Compound C does. Therefore, the incorrect example of tourmaline is **Compound A**.