Colloids around us - class-XII

Which of the following statements are correct?
(i)   When an animal hide, which has negatively charged particles, is soaked in tannin, which contains positively charged colloidal particles, mutual coagulation does not take place.
(ii) Photographic films are prepared by coating an emulsion of the light sensitive silver bromide in gelatin over glass plates or celluloid films.
(iii) Latex is a colloidal solution of rubber particles which are negatively charged.
(iv) In Cottrell precipitator, the smoke, before it comes out from the chimney, is led through a chamber containing plates having a charge opposite to that carried by smoke particles. The particles on coming in contact with these plates acquire some charge and do not get precipitated.