A: Electronic energy for hydrogen atom of different orbitals follow the sequence
` 1s lt 2s = 2p lt 3s = 3p = 3d`
R : Electronic energy for hydrogen atom depends only on n and is independent of 'l' & 'm' values .

Options

A. IF both assertion & reason are true and the reason is the correct explanation of the assertion then mark
B. IF both assertion & reason are true but the reason is not the correct explanation of the assertion , then mark
C. IF assertion is true statement but reason is false , then mark
D. If both assertion and reason are false statements then mark

Answer

To solve the question, we need to analyze both the assertion (A) and the reason (R) provided regarding the electronic energy levels of a hydrogen atom.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that the electronic energy levels for a hydrogen atom follow the sequence:
\[ 1s < 2s = 2p < 3s = 3p = 3d \]
- This means that the energy of the 1s orbital is the lowest, followed by the 2s and 2p orbitals which have the same energy, and then the 3s, 3p, and 3d orbitals which also have the same energy.

2. **Understanding the Reason (R)**:
- The reason states that the electronic energy for a hydrogen atom depends only on the principal quantum number \( n \) and is independent of the azimuthal quantum number \( l \) and the magnetic quantum number \( m \).
- For hydrogen, which is a one-electron system, the energy levels are determined solely by \( n \). This means that all orbitals with the same \( n \) value will have the same energy.

3. **Evaluating the Assertion**:
- The assertion is true because it correctly describes the energy levels of the hydrogen atom. The energy levels indeed follow the stated sequence.

4. **Evaluating the Reason**:
- The reason is also true. In a hydrogen atom, the energy levels depend only on the principal quantum number \( n \) and not on \( l \) or \( m \). This is a characteristic of hydrogen due to its single electron.

5. **Relation between Assertion and Reason**:
- The reason provides a correct explanation for the assertion. Since the energy levels depend only on \( n \), it justifies why the orbitals with the same \( n \) (like 2s and 2p, or 3s, 3p, and 3d) have the same energy.

6. **Conclusion**:
- Both the assertion and the reason are true, and the reason correctly explains the assertion. Therefore, the answer to the question is:
- **Answer: A (Both A and R are true, and R is the correct explanation of A)**.