Answer
The "Acid A" is stronger. Because its $K_a$ value is greater.
Work Step by Step
When comparing the strength of acids, the one with a higher $K_a$ value is considered stronger.
Analyzing the Ka values:
$K_a$ (Acid A) = $1 \times 10^{-5}$
and
$K_a$ (Acid Z) = $5 \times 10^{-6}$
Since $1 \times 10^{-5} > 5 \times 10^{-6}$, the "Acid A" is stronger.
