In which of the following all the electrons are paired?

Options

A. Atom with atomic number 22
B. Nitride ion
C. Atom with configuration `3s^(2) 3p^(4)`
D. In all

Explanation

To determine which of the given options has all electrons paired, we will analyze the electron configurations of each option step by step.

### Step 1: Analyze the first option - Titanium (Atomic Number 22)
- The atomic number 22 corresponds to Titanium (Ti).
- The electron configuration for Titanium is:
- 1s² 2s² 2p⁶ 3s² 3p⁶ 3d² 4s²
- Focusing on the outermost electrons:
- The 3d subshell has 2 electrons, and the 4s subshell has 2 electrons.
- According to Hund's rule, the 3d electrons will fill singly before pairing. Therefore, there are 2 unpaired electrons in the 3d subshell.
- Conclusion: Titanium has unpaired electrons.

### Step 2: Analyze the second option - Nitride Ion (N³⁻)
- The nitride ion (N³⁻) has gained 3 extra electrons.
- The atomic number of nitrogen (N) is 7, so the electron configuration for neutral nitrogen is:
- 1s² 2s² 2p³
- For the nitride ion (N³⁻), we add 3 electrons:
- 1s² 2s² 2p⁶
- The 2p subshell is now fully filled with 6 electrons (2 in 2s and 4 in 2p).
- All electrons in the nitride ion are paired.
- Conclusion: The nitride ion has all paired electrons.

### Step 3: Analyze the third option - Atomic Number 34 (Selenium)
- The atomic number 34 corresponds to Selenium (Se).
- The electron configuration for Selenium is:
- 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁴
- Focusing on the 4p subshell:
- The 4p subshell has 4 electrons.
- According to Hund's rule, the 4p electrons will fill as follows:
- 1 (unpaired) 2 (paired) 3 (unpaired) 4 (paired)
- There are 2 unpaired electrons in the 4p subshell.
- Conclusion: Selenium has unpaired electrons.

### Final Conclusion:
The only option where all electrons are paired is the **Nitride Ion (N³⁻)**.

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