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## Homework Statement

Determine if the electron transitions are "allowed" or "forbidden" using the transition rules:

i. 2p→2s

ii. 1s→2p

iii. 3d→2p

iv. 3d→1s

v. 4s→2p

## Homework Equations

Δ

*l*= ±1, Δ

*m*

_{l}= 0, ±1

E = (-2.18*10

^{-18}eV)(1/n

_{1}

^{2}- 1/n

_{2}

^{2})

## The Attempt at a Solution

I know iv. is forbidden because Δ

*l*is greater than 1, but what about the others? If i. is allowed then the energy is 0eV, which I think is not possible because photos are emitted. May anyone please offer a brief explanation to why it is allowed?

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