If the total number of neutrons present in `D_(2)O^(18)` molecules is x then the value of `(x)/(2)` is `"__"`.

Answer

To solve the problem, we need to determine the total number of neutrons in the molecule \( D_2O^{18} \) and then find the value of \( \frac{x}{2} \), where \( x \) is the total number of neutrons.

### Step-by-Step Solution

1. **Identify the components of the molecule**:
- The molecule \( D_2O^{18} \) consists of two deuterium (D) atoms and one oxygen (O) atom with a mass number of 18.

2. **Determine the neutrons in deuterium (D)**:
- Deuterium is an isotope of hydrogen with an atomic number of 1 and a mass number of 2.
- The number of neutrons in deuterium can be calculated as:
\[ \text{Neutrons in D} = \text{Mass number} - \text{Atomic number} = 2 - 1 = 1 \]
- Since there are 2 deuterium atoms in \( D_2O^{18} \):
\[ \text{Total neutrons from D} = 2 \times 1 = 2 \]

3. **Determine the neutrons in oxygen (O)**:
- The oxygen atom in this molecule has a mass number of 18 and an atomic number of 8.
- The number of neutrons in oxygen can be calculated as:
\[ \text{Neutrons in O} = \text{Mass number} - \text{Atomic number} = 18 - 8 = 10 \]

4. **Calculate the total number of neutrons in \( D_2O^{18} \)**:
- Now, we can find the total number of neutrons in the entire molecule:
\[ \text{Total neutrons} = \text{Total neutrons from D} + \text{Total neutrons from O} = 2 + 10 = 12 \]
- Therefore, \( x = 12 \).

5. **Calculate \( \frac{x}{2} \)**:
- Now, we need to find \( \frac{x}{2} \):
\[ \frac{x}{2} = \frac{12}{2} = 6 \]

### Final Answer
The value of \( \frac{x}{2} \) is **6**.