Isotopic number of `._(26)^(58)Fe` is:

Explanation

To find the isotopic number of the isotope represented as `._(26)^(58)Fe`, we will follow these steps:

### Step 1: Identify the mass number and atomic number
- The mass number (A) is given as 58.
- The atomic number (Z) is given as 26.

### Step 2: Understand the definitions
- The mass number (A) is the total number of protons (p) and neutrons (n) in the nucleus of an atom:
\[ A = n + p \]
- The atomic number (Z) represents the number of protons (p) in the nucleus:
\[ Z = p \]

### Step 3: Calculate the number of protons
From the atomic number:
- \( p = Z = 26 \)

### Step 4: Calculate the number of neutrons
Using the mass number:
- Rearranging the mass number equation gives:
\[ n = A - p \]
- Substitute the values:
\[ n = 58 - 26 \]
\[ n = 32 \]

### Step 5: Calculate the isotopic number
The isotopic number is defined as the difference between the number of neutrons and the number of protons:
\[ \text{Isotopic Number} = n - p \]
Substituting the values we found:
\[ \text{Isotopic Number} = 32 - 26 \]
\[ \text{Isotopic Number} = 6 \]

### Final Answer
The isotopic number of `._(26)^(58)Fe` is **6**.

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