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K₃PO₄ and HBr  

Explanation:

The premise of your question is incorrect.

A strong electrolyte is a substance that ionizes completely in solution.

For example, CaCO₃, is a strong electrolyte, even though it is insoluble.

Very little of it goes into solution, but every bit that does dissolve separates completely into ions.

In an ionic equation, we write it as CaCO₃(s) because it is insoluble.

An ionic equation shows soluble strong electrolytes as ions.

K₃PO₄ is a soluble strong electrolyte because salts of Group 1 metals are soluble.

HBr is a strong acid and  a strong soluble electrolyte. In aqueous solution it dissociates completely into H⁺ and Br⁻.

Acetic acid is a soluble weak electrolyte. It is a weak acid, so only a few of its molecules dissociate into ions.

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.