How many statements are correct with respect to chrysophytes? (i) They are found in the marine environment, freshwater organisms are very rare. (ii) In diatoms, the cell walls form two thick overlapping shells which fit together as in a soapbox. (iii) The cell membranes of diatoms are embedded with silica and accumulation of them over billions of years is referred to as ‘diatomaceous earth’. (iv) Diatoms are the chief ‘Producers’ in the oceans.