## Chemistry: The Molecular Science (5th Edition)

The "Acid A" is stronger. Because its $K_a$ value is greater.
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.