$\alpha=\sqrt{\frac{K_{b}}{c}}=\sqrt{\frac{1.7 \times 10^{-9}}{0.1}}=\sqrt{1.7 \times 10^{-8}}$
$\% a=1.3 \times 10^{-4} \times 100$
$=1.3 \times 10^{-2}=0.013$