Question

What is meant by negligible compressibility

Answer 1

Compressibility is the change in volume of a fluid or solid when pressure is exerted on it.

Negligible compressibility means that the substance in question cannot be compressed or the change in volume is miniscule so that it can be said to have negligible compressibility.

Gases can be easily compressed to large degrees, which is reduced when we talk about liquids and in case of solids, compressibility decreases much more. Also, the denser a substance, lesser is its compressibility. For solids, there is very little inter-molecular space (which decreases for denser solids), so they cannot be compressed easily.