A ground state gaseous atom of which element has the greatest number of unpaired electrons?

Atomic number of Arsenic is 33.

Its electronic configuration is $1{\mathrm{s}}^2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{2}3{\mathrm{d}}^{10}4{\mathrm{s}}^{2}4{\mathrm{p}}^3.$

So, it can be seen that the number of unpaired electrons in As is 3.