If the dissociation constants of two weak acids A & B are $K_1$ & $K_2$ , then the relative strengths of A & B are given by

For weak acids, dissociation constant is $K_a={\alpha }^2$

OR $\alpha =(K_a{)}^{\frac{1}{2}}$ OR $\alpha =\sqrt{K_a}$

Therefore, ratio of relative strength of 2 acids is $\frac{{\alpha }_1}{{\alpha }_2}=\sqrt{\frac{K_1}{K_2}}$.

Hence, the correct option is option 4) $\sqrt{\frac{K_1}{K_2}}$.