Answer:
The decreasing order of first ionization energy: Se > Ge > In > Cs
The decreasing order of first ionization energy: x > y > z
Explanation:
Ionization energy refers to the energy needed to completely pull out an electron from the valence shell of a neutral gaseous atom.
First ionization energy is the energy involved in the removal of first valence electron.
In the periodic table, down the group, as atomic radius of elements increases, the ionization energy decreases
Whereas, across a period, as atomic radius of elements decreases, the ionization energy increases.
PART (A):
Position of the given elements in the periodic table:
Indium (In): Group 13, period 5
Germanium (Ge): Group 14, period 4
Selenium (Se): Group 16, period 4
Caesium (Cs): Group 1, period 6
Thus, the increasing order of atomic radius: Se < Ge < In < Cs
Therefore, the decreasing order of first ionization energy: Se > Ge > In > Cs
PART (B):
Given elements:
element x: radius = 110 pm
element y: radius = 199 pm
element z: radius = 257 pm
Thus, the increasing order of atomic radius: x < y < z
Therefore, the decreasing order of first ionization energy: x > y > z