Which of the following molecular orbital has the lowest energy ?

Options

A. `sigma2p_z`
B. `sigma^** 2p_z`
C. `pi^** 2p_x`
D. `pi^** 2p_y`

Explanation

To determine which molecular orbital has the lowest energy among the given options (sigma 2pz, sigma star 2pz, pi star 2px, and pi star 2py), we can follow these steps:

### Step 1: Understand Molecular Orbitals
Molecular orbitals are formed from the combination of atomic orbitals. They can be classified as bonding or anti-bonding orbitals. Bonding orbitals are lower in energy, while anti-bonding orbitals are higher in energy.

### Step 2: Identify the Types of Orbitals
From the options provided:
- **Sigma (σ) 2pz**: This is a bonding molecular orbital.
- **Sigma star (σ*) 2pz**: This is an anti-bonding molecular orbital.
- **Pi star (π*) 2px**: This is also an anti-bonding molecular orbital.
- **Pi star (π*) 2py**: This is another anti-bonding molecular orbital.

### Step 3: Compare Energy Levels
- Bonding molecular orbitals (like σ 2pz) are more stable and have lower energy compared to anti-bonding molecular orbitals (like σ* 2pz, π* 2px, and π* 2py).
- Anti-bonding molecular orbitals have higher energy due to the repulsion between the atomic orbitals that form them.

### Step 4: Conclusion
Since there is only one bonding molecular orbital (σ 2pz) among the given options, it will have the lowest energy compared to the three anti-bonding orbitals.

### Final Answer
The molecular orbital with the lowest energy is **sigma (σ) 2pz**.

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