Which of the following transitions is not allowed in the normal electronic emission spectrum of an atom?

Question

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Selection rule for electronic transitions:

The quantum mechanical selection rule requires  for allowed transitions.

Evaluating each option:

- (a)  :  → Forbidden by  rule. However, this is also not observed.

- (b)  :  ✓ → Allowed (Lyman series).

- (c)  :  ✓ ( is fine), but this is an emission transition from  to . In emission, the electron must go to lower energy (lower ). Going from  to  is absorption, not emission. This transition is not allowed in emission spectrum. ✗

- (d)  :  ✓, and

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