Question

A block of wood floats in water with 4/5th of its volume submerged

Answer 1

your question is incomplete. A complete question is -----> A block of wood floats in water with 4/5 th of its volume submerged , but it just floats in a liquid . What is the density of the liquid ?

Let the density of liquid is d.
we know, density of water is 1000 kg/m³

a/c to question,
the block of wood floats in water with 4/5 th of its volume submerged. but it just floats in a liquid.
from Archimedes principle,
$\rho(liquid)=\frac{4}{5}\rho(water)$
= 4/5 × 1000 kg/m³
= 800 kg/m³