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www.GOALias.blogspot.com(iii)(iv)Both processes A and B are chemical changes.None of these processes is a chemical change.Extended Learning — Activities and Projects1. Describe two changes that are harmful. Explain why you consider themharmful. How can you prevent them?2. Take three glass bottles with wide mouths. Label them A, B and C. Fillabout half of bottle A with ordinary tap water. Fill bottle B with waterwhich has been boiled for several minutes, to the same level as in A. Inbottle C, take the same boiled water and of the same amount as in otherbottles. In each bottle put a few similar iron nails so that they are completelyunder water. Add a teaspoonful of cooking oil to the water inbottle C so that it forms a film on its surface. Put the bottles away for afew days. Take out nails from each bottle and observe them. Explainyour observations.3. Prepare crystals of alum.4. Collect information about the types of fuels used for cooking in yourarea. Discuss with your teachers/parents/others which fuels are lesspolluting and why.Did you know?Near the Qutub Minar in Delhistands an iron pillar (Fig. 6.7)which is more than 7 metreshigh. It weighs more than 6000 kg.It was built more than 1600 yearsago. After such a long period it hasnot rusted. For its quality of rustresistance it has been examinedby scientists from all parts of theworld. It tells something about theadvances India had made inmetal technology as back as1600 years ago.Fig. 6.7 Iron pillarPHYSICALAND CHEMICALCHANGES6767