Question

Solve question number 20 . Give reasons in detail....

Answer 1

See firstly u should know what does ionization enthalpy mean:

Ionization Enthalpy: is defined as the amount of energy required to remove the most loosely bonded electron or valence electron from the outermost shell of an isolated gaseous atom.

Then you should know the trends that ionization energy have across a period and down a group,
 
So, "Ionization Energy across a period increases", this is because when we move across a period the atomic size or u can radius decreases and since ionization energy is the energy required to remove a loosely bounded electron from the outermost shell and if the size of the atom would be small thus all the electrons would be closely bounded to the nucleus also the shielding effect or screening effect will be very high i.e. the electrons would be more greatly attracted to the nucleus and thus the energy required to remove that electron would be very high thus ionization enthalpy would also be very high thus the element X with ionization enthalpy as 500KJ would be present on the rightmost part of the periodic table.

Now, "Ionization Enthalpy down the group decreases", this is because as we move down the group the atomic size or radius increases and thus the valence/outermost electrons would be loosely bounded to the nucleus due to less shielding effect and thus the energy required to remove that electron will be comparatively less and thus the ionization enthalpy would also be less thus the element Y must be present somewhere down the group as compared to element X.

HOPE YOU GET IT.........