The correct order of energy of 2s orbitals of following is :

Q: The correct order of energy of 2s orbitals of following is :

The correct order of energy of 2s orbitals of following is :

Question

Accepted Answer

The correct order of energy of 2s orbitals for the elements given in Option 1 is $H>Li>Na>K$. Let's explore why this is the correct order and why the other options are incorrect.

### Explanation for Option 1: $H>Li>Na>K$

1. **Hydrogen (H):** In hydrogen, the 2s orbital is not occupied in the ground state, but if we consider an excited state where the electron is in the 2s orbital, it will have the highest energy compared to the other elements listed. This is because hydrogen has only one electron and no electron-electron repulsion, leading to a higher energy level for the 2s orbital.

2. **Lithium (Li):** In lithium, the 2s orbital is occupied by the second electron. The presence of two electrons in lithium introduces electron-electron repulsion, which slightly lowers the energy of the 2s orbital compared to hydrogen.

3. **Sodium (Na):** Sodium has more electrons and a larger atomic size than lithium. The increased shielding effect and electron-electron repulsion in sodium further lower the energy of the 2s orbital compared to lithium.

4. **Potassium (K):** Potassium has an even larger atomic size and more electrons than sodium. The increased shielding and electron-electron repulsion in potassium result in the lowest energy for the 2s orbital among the elements listed.

### Explanation for Incorrect Options:

- **Option 2: $K>Na>Li>H$**
  - This option suggests that the energy of the 2s orbital increases from potassium to hydrogen, which contradicts the trend of increasing atomic size and electron shielding. As atomic size increases, the energy of the 2s orbital decreases due to increased electron shielding and repulsion.

- **Option 3: $H>Na>K>Li$**
  - This option incorrectly places lithium as having the lowest energy 2s orbital. As explained, lithium should have a higher energy 2s orbital than sodium and potassium due to less electron shielding and repulsion.

- **Option 4: $Na>K>Li>H$**
  - This option incorrectly suggests that sodium and potassium have higher energy 2s orbitals than lithium and hydrogen. However, due to increased atomic size and electron shielding, the energy of the 2s orbital decreases from lithium to potassium.

In conclusion, Option 1 correctly reflects the order of energy of the 2s orbitals based on atomic size, electron shielding, and electron-electron repulsion.