Why does an object float or sink when placed on the surface of water?

Why does a block of plastic released under water come up to the surface of water?

An object is placed one by one in three liquids having different densities. The object floats with $\frac{1}{9}$, $\frac{2}{11}$, and $\frac{3}{7}$ parts of its volume outside the liquid surface in liquids of densities $d_1$, $d_2$, and $d_3$ respectively. Which of the following statements is correct?

In what direction does the buoyant force on an object immersed in a liquid act?

The volume of $50\, g$ of a substance is $20\, cm^3$. If the density of water is $1\, g\, cm^{-3}$,will the substance float or sink?

Raman along with his family visited the Dead Sea. There,his father observed a lady lying on her back in the sea and reading a newspaper. This astonished Raman's father,who thought the lady might be practicing black magic. Raman explained to his father why the lady was not drowning.
$(a)$ What,according to you,is the reason the lady is not drowning in the Dead Sea?
$(b)$ What value is exhibited by Raman?