(a) A lyophilic sol is stable due to the charge and the hydration of the sol particles. Such a sol can only be coagulated by removing the water and adding solvents like alcohol, acetone, etc. and then an electrolyte. On the other hand, a lyophobic sol is stable due to charge only and hence it can be easily coagulated by adding small amount of an electrolyte.
(b) The colloidal particles get precipitated, i.e., ferric hydroxide is precipitated.
(c) The atmospheric particles of colloidal range scatter blue component of the white sunlight preferentially. That is why the sky appears blue.