Question

Which of the following elements have the lowest value of $I{E}_1$?

• A. $Pb$
• B. $Sn$
• C. $Si$
• D. $C$

Answer 1

Answer: (B)

$Sn$

$C,Si,Sn.Pb$ belongs to the same group (group 4). Within a group, the ionization energy decreases from top to bottom because of the screening effect of inner electrons which reduces the effective nuclear charge on the valence electrons.

The ionization energy decreases regularly down the group; $Pb$, however, shows a higher value than $Sn$ due to poor shielding/screening of inner f-orbitals as a result of which effective nuclear charge experienced by outer shell electrons becomes more in $Pb$.

Therefore the order of ionization energy of group 4 is:

$C>Si>Pb>Sn$

Option B is correct.