The number of unpaired electrons in carbon atom in excited state is

${\mathrm{C}}_6=1{\mathrm{s}}^2,2{\mathrm{s}}^{2}2{\mathrm{p}}^2\text{ (Ground state) }$
$=1{\mathrm{s}}^2,2{\mathrm{s}}^1,2{\mathrm{p}}_{\mathrm{x}}^{1}2{\mathrm{p}}_{\mathrm{y}}^{1}2{\mathrm{p}}_{\mathrm{z}}^1\text{ (Excited state) }$
In excited state no. of unpaired electron is 4.