Osmium has atomic number 76. A particular isotopes of osmium has an atomic mass of 186.956u. Which symbol correctly represents this isotope?

Options

A. `""_(111)^(187)Os`
B. `""_(187)^(76)Os`
C. `""_(76)^(111)Os`
D. `""_(76)^(187)Os`

Answer

To represent the isotope of osmium with atomic number 76 and atomic mass 186.956 u, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Atomic Number (Z)**: The atomic number of osmium is given as 76. This number represents the number of protons in the nucleus of the atom.

2. **Identify the Atomic Mass (A)**: The atomic mass of the specific isotope of osmium is given as 186.956 u. This value represents the total number of protons and neutrons in the nucleus.

3. **Write the Isotope Symbol**: The general notation for an isotope is represented as:
\[ \text{X}^A_Z \]
where X is the chemical symbol of the element, A is the atomic mass, and Z is the atomic number.

4. **Substitute the Values**: For osmium (symbol: Os), we substitute the values:
- X = Os
- A = 186.956
- Z = 76

Therefore, the isotope can be represented as:
\[ \text{Os}^{186.956}_{76} \]

5. **Final Representation**: The correct symbol for the isotope of osmium with atomic mass 186.956 u is:
\[ \text{Os}^{186.956} \]

### Conclusion:
The correct representation of the isotope of osmium is \( \text{Os}^{186.956} \).

---