Which atom does contain `3d^1` subshell?

Answer

To determine which atom contains the `3d^1` subshell, we can follow these steps:

### Step 1: Understand Electron Configuration
The `3d` subshell is part of the d-block elements in the periodic table. The d-block elements start filling their d-orbitals after the s-orbitals of the next principal energy level have been filled.

### Step 2: Identify the Order of Filling
According to the Aufbau principle, the order of filling of orbitals is as follows:
1. 1s
2. 2s
3. 2p
4. 3s
5. 3p
6. 4s
7. 3d
8. 4p
9. 5s
10. 4d
11. 5p
12. 6s
13. 4f
14. 5d
15. 6p
16. 7s
17. 5f
18. 6d
19. 7p

### Step 3: Determine the Atomic Number for `3d^1`
The `3d^1` subshell indicates that there is one electron in the 3d subshell. To find the atomic number of the element that has this configuration, we need to consider the total number of electrons that fill the orbitals before `3d`.

- The filling sequence up to `3d` is:
- 1s² (2 electrons)
- 2s² (2 electrons)
- 2p⁶ (6 electrons)
- 3s² (2 electrons)
- 3p⁶ (6 electrons)
- 4s² (2 electrons)

Adding these gives us:
2 + 2 + 6 + 2 + 6 + 2 = 20 electrons

### Step 4: Add the Electron in `3d`
Since `3d^1` means there is one electron in the 3d subshell, we add this to the total:
20 + 1 = 21

### Step 5: Identify the Element
The atomic number 21 corresponds to the element Scandium (Sc). Therefore, the atom that contains the `3d^1` subshell is Scandium.

### Final Answer
The atom that contains the `3d^1` subshell is Scandium (Sc).

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