The partial electron configuration of an atom with 12 electrons is shown.

1s22s22p6X

Which of the following does X represent?

2d2

3s2

3p2

4s2

The correct answer is 3s2

I believe this is the electric configuration for magnesium, so, In writing the electron configuration for Magnesium the first two electrons will go in the 1s orbital. Since 1s can only hold two electrons the next 2 electrons for magnesium go in the 2s orbital. The next six electrons will go in the 2p orbital. The p orbital can hold up to six electrons. We'll put six in the 2p orbital and then put the remaining two electrons in the 3s. Therefore the Magnesium electron configuration will be 1s22s22p63s2.

The answer is B