PLACE are usually irreversibleHave an effect on the chemical bondsEXAMPLE - Digestion of food Burning of PAPER Corrosion of an iron nail Physical Change:A physical change is a change that doesn't affect the chemical composition of the substanceNo new products are formedThe changes taking place are usually reversibleHave no effect on the chemical bonds sometimes, only the state of matter is changed.EXAMPLE -TEARING of papermelting of iceExplanation -In the question, two changes are being talked about, 1. Cotton to a bedsheet - As cotton is being changed to a cotton bedsheet there is no change in the chemical properties of the cotton.The raw cotton is just molded into thin FIBERS and then to a big bedsheet.Hence, cotton remained cotton.So it is a physical change2. WAX to the production of light -Here we are not talking about the melting of wax we are also talking about the concept of burning or lighting of the was which is a chemical change as the wick is being burned to convert into heat and lightThe wax has now been converted to produce heat and light. Chemical changes are being seen hence it is a chemical change. The correct answer Cotton to a bed sheet is a physical change and Wax to the production of light is a Chemical change.