Three different particles have the same electron configuration one is a cation of an alkali metal one is an anion of the halide in the third period and the third particle is an atom of a noble gas what are the identity of the three particles which particle should have the smallest atomic radius which should have the largest and why

The hint here is: anion of the halide in the third period. Halides are elements found in group 7. Thus, the halide referred to here is Chloride, Cl⁻. Thus, the noble gas (elements in group 8) and the alkali metal (elements in group 1) that has a similar electronic configuration are Argon and Potassium ion. 

1. The three different particles having the same electronic configuration are: Potassium ion, Chloride ion and Argon.

2. Anions will always be larger than cations of the same electronic configuration. So, the largest atomic radius would be the Chloride ion, while the smallest would be the Potassium ion. The Argon is right in between.

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 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.

If this is a true or galse then its true but if not then what is the question?