Hint: In chemistry, periodic tables play a vital role. In the periodic table totally \[118\] elements. In the periodic table totally \[18\] columns and \[7\] rows. The columns are called groups. Hence, \[18\] groups in the periodic table. The rows are called as period. Hence, totally \[7\] period in the table. The atomic number of the element is nothing but the number of electrons or number of protons. The mass number of the atom is nothing but the sum of number of protons and number of neutrons.
Complete answer: We have to remember that the isoelectronic is nothing but the two or more atoms having the same number of electrons in their ionic state. Here main is stability of the atom or octet rule. Octet rule is different for atoms. The octet rule is used to identify the stable electronic configuration of the atom. But it depends on the outer shell of the atom. Example of isoelectronic, Examples of isoelectronics are chloride ion, potassium ion argon. All have the same number of electrons in the outermost shell of the atom. Argon generally has eighteen electrons in the outermost shell of an atom. But chlorine accepts the one electron of the other atom to attain eighteen electrons in the outermost shell. But in the potassium case, it sacrifices one electron to attain eighteen electrons in the outermost shell of the atom. Now all the three atoms are having the same electrons in the outermost shell. That the above all states of atoms are considered isoelectronic species.
Note: We must have to know that in chemistry each element has a specific symbol in the periodic table. Inside the atom having electrons, protons and neutrons. The electrons revolve around the nucleus in the atom. The neutrons and protons are present inside the nucleus. The electrons are arranged in the energy level of the shell in the atom.