A metal has electronic configuration `[Ar]^(18)3d^7 4s^2`.On the basis of this electronic configuration find out the group number.

Explanation

To determine the group number of the metal with the electronic configuration `[Ar] 3d^7 4s^2`, we can follow these steps:

### Step 1: Identify the total number of electrons
The electronic configuration `[Ar] 3d^7 4s^2` indicates that the element has:
- 18 electrons from Argon (Ar)
- 7 electrons in the 3d subshell
- 2 electrons in the 4s subshell

Total number of electrons = 18 + 7 + 2 = 27.

### Step 2: Identify the element
The total number of electrons (27) corresponds to the atomic number of the element. The element with atomic number 27 is Cobalt (Co).

### Step 3: Determine the group number
Cobalt (Co) is a transition metal. Transition metals are found in groups 3 to 12 of the periodic table.

To find the specific group number:
- The d-block elements (transition metals) are characterized by their d electrons.
- Cobalt has 7 d electrons (3d^7) and is located in the 9th group of the periodic table.

### Conclusion
Therefore, the group number for the metal with the electronic configuration `[Ar] 3d^7 4s^2` is **9**.

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