Explain why pure liquids and solids can ignored while writing the equilibrium constant expression?

Explanation

For the concentration of pure solid or pure liquid,
[Solid] or [Liquid] =`"No. of moles"/"Volume in L"="Mass/Molar mass"/"Volume"`
`="Mass"/"Volume"xx1/"Molar mass" ="Density" xx 1/"Molar mass"`
Since density of pure solid or liquid is constant at constant temperature and molar mass is also constant therefore, their molar concentrations are constant.