Question

Which of the following electron configurations represents an atom of magnesium in an excited state?

• A. $1s^{2}2s^{2}2p^6$
• B. $1s^{2}2s^{2}2p^{6}3s^2$
• C. $1s^{2}2s^{2}2p^{5}3s^{2}3p^2$
• D. $1s^{2}2s^{2}2p^{6}3s^{1}3p^1$

Answer 1

The correct option is D $1s^{2}2s^{2}2p^{6}3s^{1}3p^1$

$1s^{2}2s^{2}2p^{6}3s^{1}3p^1$ represents an atom of magnesium in an excited state.
The ground state electronic configuration is $1s^{2}2s^{2}2p^{6}3s^2$. One electron is transferred from 3s to 3p level to form excited state. Mg has atomic number of 12. Thus it will have 12 electrons.