Question

I.P of sodium is $5.14\,ev$ then I.P of potassium will be:
1. Equal to sodium
2. $5.68\,\,ev$
3. $4.34\,ev$
4. $10.28\,ev$

Answer 1

Hint: We know the modern periodic table is based on the properties of elements as function of their atomic number. The properties are based on the electronic configuration of the elements. Periodic properties are the trend in properties across a period from left to right to down the group. Some of the important periodic properties are metallic character, non-metallic character, atomic size, electron affinity, ionization potential and electronegativity.

Complete step by step answer:
I.P stands for ionization potential. We can define ionization potential as the amount of energy that is necessary to remove an electron from the valence shell of a gaseous atom and turn it to a positively charged gaseous ion. It is opposite to electronegativity. Lower the energy, more readily an atom turns to a cation.
In the periodic table, we can observe that elements present on the right side of the periodic table contain higher ionization energy because their outermost shell is completely filled. We can also observe that elements present on the left side of the periodic table would have less ionization energies because they tend to lose more readily and turn to cations. Thus, ionization energy increases from left to right in the periodic table.
Electron shielding also affects the ionization energy. The ability of an atom’s inner electron to shield its positively charged nucleus from its outermost electron is called electron shielding. On moving to the right of a period, there is an increase in the number of electrons and shielding also increases. Because of this increasing shielding effect, it is easier to ionize the valence shell electrons, and therefore, ionization energy decreases down a group.
We know that sodium and potassium belong to different periods but in the same group.
Sodium belongs to the third period and potassium belongs to the fourth period. On moving down the group, ionization energy decreases. Therefore, the ionization potential of potassium will be smaller than that of sodium.

$\therefore $Option (C) is correct.

Note:
We have to remember that the ionization potential of noble gases is highest due to the completely filled outermost shells. Helium has the highest ionization potential than all elements. Some elements have various ionization potentials called as first ionization energy, second ionization energy, third ionization energy etc. There is a decrease in the ionization potential with increase in atomic radii.