Answer
(b) $p_{u}=\frac{3}{2}p_{b}$
Work Step by Step
If $p_{u}$ is the density of the unknown liquid,
$p_{b}$ is the density of the block,
Weight of the block = weight of liquid displaced by block
So,
$p_{b}Vg=p_{u}\frac{2}{3}Vg$
So,
$p_{u}=\frac{3}{2}p_{b}$
