Question

A solid weighs 75 g in air and 55.6 g in water. Find the relative density.

Answer 1

the relative density is 123g

Answer 2

Archimedes: When a body is immersed in a fluid it undergoes a loss in mass equivalent to the mass of fluid displaced . 

Loss in mass = 75g - 55.6= 19.4g H2O displaced 
Density of water = 1g/mL 
Therefore the object displaced 19.4mL of water = volume of the object . 
Relative density when kept in water = mass / volume 
Relative density =55.6 / 19.6mL 
Relative density = 2.836/mL