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

Concentration of solid or pure liquid,

[substance] =

=

=

Since density and molar mass doesn’t vary, concentration of the substance remains constant.

Pure liquids and solid have a constant concentration. Composition of solids remain same throughout a reaction even though amount may change.

Similarly, pure liquids have same composition (since it has only one substance)