The mass of acetic acid present in $500ml$ solution in which it is 1% ionized $\left(K_a\text{of}C{H}_{3}COOH=1.8\times {10}^{-5}\right)$

     $K_a=C.{\alpha }^2$

$\Rightarrow C=\frac{K_a}{{\alpha }^2}$

          $=\frac{1.8\times {10}^{-5}}{{\left({10}^{-2}\right)}^2}$

           $=1.8\times {10}^{-1}$

            $=0.18M$

Weight of acetic acid$=\frac{M\times GMW\times V}{1000}$

                                     $=\frac{0.18\times 60\times 500}{1000}=5.4gm$