Identify the element having lowest first ionization enthalpy.
Identify the element having lowest first ionization enthalpy.
Po
Te
Br
Kr
Solution
The ionization enthalpy (I.E) decreases down the group due to increase in the atomic size. Therefore, I.E of Te is more than that of Po. Across a period, I.E increases with increase of atomic number.
Therefore, I.E of Br and Kr is in the order: $\mathrm{Br} \lt \mathrm{Kr}$.
Hence, the correct decreasing order of I.E for the given elements is: $\mathrm{Kr}\gt\mathrm{Br}\gt\mathrm{Te}\gt\mathrm{Po}$