Answer
Please see the work below.
Work Step by Step
We can neglect x if $\frac{C_a}{K_a}>=100$. In the given scenario,$\frac{C_a}{K_a}=\frac{0.0010}{6.8\times 10^{-4}}=1.47$ which is less than 100 so x cannot be neglected and thus the degree of ionization is significant.