# How many electrons are in the outermost principal energy level (shell) of an atom of carbon in the ground state?

For carbon, $Z = 6$, and thus its electronic configuration is................
$C : 1 {s}^{2} 2 {s}^{2} 2 {p}^{2}$. The valence shell of carbon (for which $n = 2$) thus contains 4 electrons. Of course there are various hybridization schemes, but the fact remains that carbon commonly forms $C {H}_{4}$ and $C {R}_{4}$ molecules, i.e. utilizing 4 valence electrons.