write the electron configuration for a neutral atom of magnesium.

Explanation:

Step1: Determine magnesium's atomic number

Magnesium has an atomic number of 12, so a neutral atom has 12 electrons.

Step2: Fill electron - shells and sub - shells

We fill the shells and sub - shells according to the Aufbau principle. First, the 1s sub - shell can hold 2 electrons: $1s^{2}$. Then the 2s sub - shell can hold 2 electrons: $2s^{2}$. Next, the 2p sub - shell can hold 6 electrons: $2p^{6}$. Finally, the remaining 2 electrons go into the 3s sub - shell: $3s^{2}$.

Answer:

$1s^{2}2s^{2}2p^{6}3s^{2}$