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

Explanation

[Pure liquid] or [Pure solid] = No. of moles/ Volume in L = Mass/moLmass/Volume = Mass/Volume `xx` 1/Molmass = Density/Molmass
As density of a pure liquid and pure solid is constant at constant temperature and molecular mass is also constant, therefore, their molar concentrations are constant and included into the equilibrium constant.