Answer
$Ge$ has smaller 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).
$Ge$ is in group 4A and fourth period. $Cl$ is in group 7A and third period.
Considering their positions, $Cl$ is to the right and upper of $Ge$. Both of these positions support a higher first ionization energy, which means $Cl$ has a higher first ionization energy than $Ge$.
So $Ge$ has lower first ionization energy.