Answer
$Ge$ has lower first ionization energy.
Work Step by Step
The periodic trend of the first ionization energy:
- Going from left to right across a period, the first ionization energy increases (since effective nuclear charge increases and atomic radii decrease).
- Going from up to down in a group, the first ionization energy decreases (since effective nuclear charge only increases slightly but atomic radii increase largely).
$S$ is in group 6A and third period. $Ge$ is in group 4A and fourth period.
Considering their positions, $S$ is to the right and upper of $Ge$. Both of these positions support a higher first ionization energy, which means $S$ has a higher first ionization energy than $Ge$.
So $Ge$ has lower first ionization energy.
