Question

how will you find the density of an irregular solid​

Answer 1

The density of something is just the mass divided by the volume:

D = m/V

The mass you can measure on a balance or a scale, and the volume is the amount of space the object occupies. You can find the volume of an irregular object by immersing it in water in a beaker or other container with volume markings, and by seeing how much the level goes up.

You can use this relation backwards too -- if you know what material an object is made of, you can look up its density in a book. Measuring its mass allows you to compute the volume.