b
(b)Upthrust = weight of body
For \(A\) , \(\frac{{{V_A}}}{2} \times {\rho _W} \times g = {V_A} \times {\rho _A} \times g \Rightarrow {\rho _A} = \frac{{{\rho _W}}}{2}\)
For \( B\), \(\frac{3}{4}{V_B} \times {\rho _W} \times g = {V_B} \times {\rho _B} \times g \Rightarrow {\rho _B} = \frac{3}{4}{\rho _W}\)
(Since 1/4 of volume of B is above the water surface)
\(\frac{{{\rho _A}}}{{{\rho _B}}} = \frac{{{\rho _W}/2}}{{3/4\;{\rho _W}}} = \frac{2}{3}\)