The electronic configuration of an atom is as follows `1s^(2) 2s^(2) 2p^(2)`
a) Which element's atom is it ?
b) What is the valence shell ?
c) When excited what could be the number of lone / single electrons in this atom ?
d) What is the value of principal quantum numbers of two electrons in the first box ?

Explanation

Given electronic configuration of atom is `1 s^(2) 2s^(2) 2p^(2)`.
a) The element is carbon.
b) The valence shell is L `(2s^(2) 2p^(2))`
c) In excited state the electron in 2s orbital enters orbital . So it has 4 unpaired electrons .
d) The value of principal quantum number is 1.