Answer
$Ba$ has lower 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).
$Ti$ is in group 4B and fourth period. $Ba$ is in group 2A and sixth period.
Considering their positions, $Ti$ is to the right and upper of $Ba$. Both of these positions support a higher ionization energy, which means $Ti$ has a higher ionization energy than $Ba$.
So $Ba$ has lower ionization energy.
