Which of the following is not a member of 3d-transition series ?

Options

A. Fe
B. Co
C. Au
D. Cu

Explanation

To determine which of the following elements is not a member of the 3d-transition series, we first need to understand what the 3d-transition series is.

### Step 1: Define the 3d-transition series
The 3d-transition series consists of transition metals that have atomic numbers ranging from 21 to 30. These elements are located in the d-block of the periodic table.

### Step 2: Identify the elements in the 3d-transition series
The elements in the 3d-transition series are:
- Scandium (Sc) - Atomic number 21
- Titanium (Ti) - Atomic number 22
- Vanadium (V) - Atomic number 23
- Chromium (Cr) - Atomic number 24
- Manganese (Mn) - Atomic number 25
- Iron (Fe) - Atomic number 26
- Cobalt (Co) - Atomic number 27
- Nickel (Ni) - Atomic number 28
- Copper (Cu) - Atomic number 29
- Zinc (Zn) - Atomic number 30

### Step 3: Analyze the options given in the question
Now, we need to check the atomic numbers of the given options to see which one does not belong to the range of 21 to 30.

1. **Iron (Fe)** - Atomic number 26 (in the 3d series)
2. **Cobalt (Co)** - Atomic number 27 (in the 3d series)
3. **Copper (Cu)** - Atomic number 29 (in the 3d series)
4. **Gold (Au)** - Atomic number 79 (not in the 3d series, it belongs to the 5d series)

### Step 4: Conclusion
From the analysis, we can conclude that Gold (Au) is not a member of the 3d-transition series. Therefore, the correct answer is:

**Gold (Au)**

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