The general configuration for elements of group 9 is

Options

A. `(n-1) d^(6) ns^(2)`
B. `nd^(7) ns^(2)`
C. `(n-1)d^(2) ns^(2) np^(6)`
D. `(n-1) d^(7) ns^(2)`.

Explanation

To determine the general electron configuration for elements of group 9, we can follow these steps:

### Step 1: Identify the Elements in Group 9
Group 9 of the periodic table includes elements such as cobalt (Co), rhodium (Rh), and iridium (Ir).

### Step 2: Write the Electron Configuration for Cobalt
Cobalt has an atomic number of 27. The electron configuration for cobalt can be written as:
- 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁷

### Step 3: Identify the Outermost Electrons
In the electron configuration of cobalt, the outermost electrons are in the 4s and 3d subshells. The 4s subshell has 2 electrons and the 3d subshell has 7 electrons.

### Step 4: Generalize the Configuration for Group 9
For elements in group 9, the general electron configuration can be expressed as:
- (n-1)d⁷ ns²
Where:
- n is the principal quantum number of the outermost shell (for cobalt, n=4).
- The d subshell has 7 electrons.

### Step 5: Write the General Configuration
Thus, the general electron configuration for elements of group 9 can be summarized as:
- (n-1)d⁷ ns²

### Final Answer
The general configuration for elements of group 9 is:
- (n-1)d⁷ ns²

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