assuming that your periodic table has eighteen columns, you should highlight the four elements in the third column from the left of the table.
explanation
neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the 
have energy higher than those in the 
orbital while lower than those of the 
orbital.
by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the 
orbital is therefore filled right after 
orbitals and before 
orbitals.
potassium has electron configuration ![[\text{ar}] 4 s^{1}](/tex.php?f=[\text{ar}] 4 s^{1})
and calcium ![[\text{ar}] 4 s^{2}](/tex.php?f=[\text{ar}] 4 s^{2})
. the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration ![[\text{ar}] 4 s^{2} \; 3d^{1}](/tex.php?f=[\text{ar}] 4 s^{2} \; 3d^{1})
and satisfy the requirements.
a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the  p^{1})
and should be highlighted as well.
