Would someone me with my chemistry? you

Ionic radii of cations:

When you form a metal cation, you are removing the outermost electrons and revealing the inner core.  

For example, to form an Na⁺ ion you must remove a 3s electron from an Na atom, exposing the 2s and 2p subshells.

The n = 2 shell is smaller than an n= 3 shell, so an Na⁺ ion is smaller than an Na atom (as in the image below).

Ionic radii of anions:

When you form an anion, you are adding electrons to the outermost shell. These electrons (a) increase the shielding from the nucleus and (b) repel all the other electrons.  

The decreased nuclear attraction and the electronic repulsions cause the electron cloud to expand, so a Cl⁻ ion is larger than a Cl atom.

assuming that your periodic table has eighteen columns, you should highlight   the four elements in the third column from the left of the table.

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 and calcium . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration 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 and should be highlighted as well.

a corroding iron, if that's one of your choices