Several polyhalogen compounds were once widely used but are now restricted. Which of the statements below about them are correct?

• Statement I: Chloroform is slowly oxidised by air in the presence of light to a poisonous gas, phosgene.
• Statement II: Carbon tetrachloride released into the air helps rebuild the ozone layer.
• Statement III: DDT is not metabolised quickly by animals and builds up in their fatty tissue.
• Statement IV: Freons are quickly decomposed near the earth's surface and rarely reach the stratosphere.