In the long or modern form of the periodic table, the element in the periodic table have been divided into four blocks, `s-p-d`-and `f`-. Each period begins with the filling of new energy shell. Two series of `f`-block elements are placed at the bottom of the periodic table.
If the elements were discovered in future in which the electrons would be present in `g`-orbitals. Then `g`-orbital starts, and ends up with what atomic number?

Options

A. `121,139`
B. `121,138`
C. `122,140`
D. `122,139`

Explanation

To determine the atomic numbers at which the `g`-orbitals start and end, we can follow these steps:

### Step 1: Understand the Position of `g`-Orbitals
The `g`-orbitals are expected to be filled after the `f`-block elements in the periodic table. The `f`-block elements are located at the bottom of the periodic table and correspond to the filling of the `4f` and `5f` orbitals. The `g`-orbitals will be filled in the next period after the `f`-block.

### Step 2: Identify the Starting Point for `g`-Orbitals
The `g`-orbitals will start filling in the 8th period of the periodic table. The last element in the 7th period is Oganesson (Og), which has an atomic number of 118. The filling order of orbitals is as follows:
1. `ns`
2. `(n-2)f`
3. `(n-1)d`
4. `np`

After the completion of the 7th period, the next element (the first to fill the `g`-orbital) will be in the 8th period.

### Step 3: Determine the Electronic Configuration
The first element in the `g`-block will have the following electronic configuration:
- It will start with `8s^2` (filling the `s` orbital first).
- Then, it will fill the `5g` orbitals, which corresponds to `(n-3)g` where `n=8`.

Thus, the electronic configuration for the first `g`-block element will be:
- `8s^2 5g^1`

### Step 4: Calculate the Atomic Number
The atomic number for the first element in the `g`-block can be calculated as follows:
- The atomic number of Oganesson (118) + 3 (for `8s^2` and `5g^1`) = 121.

### Step 5: Determine the Ending Point for `g`-Orbitals
The `g`-orbitals can hold a maximum of 18 electrons. Therefore, starting from atomic number 121:
- The last element that can fill the `g`-orbitals will be `121 + 18 - 1 = 138`.

### Conclusion
Thus, the `g`-orbitals start at atomic number **121** and end at atomic number **138**.

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