In equilibrium position, let l be the length of the block immersed in the liquid as shown in figure.
Then, mg = Alρg
Or m = Alρ
If the block is given a further downward displacement y, then effective upward force (i.e. restoring force) on block is
it means F ∝ y and it is directed towards equilibrium position. Therefore, if the block is left free, it will executes SHM mass of block = m = inertia factor spring factor = Aρg