Answer
$Ca$ 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).
$Be$ and $Ca$ both belong to the same 2A group. From up to down, $Be$ appears first, then comes $Ca$. Therefore, the first ionization energy would decrease from $Be$ to $Ca$.
So $Ca$ has smaller first ionization energy.