Question

why does the solution of nacl not show tyndal effect where as the mixture of water and milk shows?

Answer 1

Solutions have tiny particles and hence don't show tyndal effects. Nacl in water is a solution which don't show tyndal effect.
Colloidal solutions show tyndal effect because the particles are comparatively bigger in size. Mixture of water and milk forms a colloidal solution which shows tyndal effect.