Einstenium has 11 electrons in the `4f` subshell. The number of unpaired electrons in the subshell is:

Options

A. 3
B. 4
C. 7
D. 11

Answer

To determine the number of unpaired electrons in the 4f subshell of Einsteinium, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Number of Electrons**:
Einsteinium has 11 electrons in the 4f subshell.

2. **Understand the Structure of the f Orbital**:
The f subshell consists of 7 orbitals. Each orbital can hold a maximum of 2 electrons (one with spin-up and one with spin-down).

3. **Fill the Orbitals According to Hund's Rule**:
According to Hund's rule, each of the 7 orbitals will be filled singly before any pairing occurs. Therefore, we will first place one electron in each of the 7 orbitals.

- After placing 7 electrons, we have 4 electrons remaining (11 total - 7 filled = 4).

4. **Pair the Remaining Electrons**:
After the first 7 electrons occupy the 7 orbitals, we start pairing the remaining electrons:
- The next electron (8th) will pair with the first orbital.
- The 9th electron will pair with the second orbital.
- The 10th electron will pair with the third orbital.
- The 11th electron will go into the fourth orbital.

5. **Count the Unpaired Electrons**:
After filling and pairing, we can visualize the occupancy of the orbitals:
- Orbital 1: 2 electrons (paired)
- Orbital 2: 2 electrons (paired)
- Orbital 3: 2 electrons (paired)
- Orbital 4: 1 electron (unpaired)
- Orbital 5: 1 electron (unpaired)
- Orbital 6: 1 electron (unpaired)
- Orbital 7: 0 electrons

Therefore, the number of unpaired electrons is 3 (from the 4th, 5th, and 6th orbitals).

### Final Answer:
The number of unpaired electrons in the 4f subshell of Einsteinium is **3**.

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