Collect information about the types of fuels used for cooking in your area. Discuss with your teachers/parents/others which fuels are less polluting and why ?

Anaerobic bacteria digest animal waste and produce biogas (Change - A). The biogas is then burnt as fuel (Change - B). The following statements pertain to these changes. Choose the correct one.

(i) Process - A is a chemical change.

(ii) Process -B is a chemical change.

(iii)Both processes A and B are chemical changes .

(iv) None of these processes is a chemical change.

Describe two changes that are harmful. Explain why you consider them harmful? How can you prevent them?

Take three glass bottles with wide mouths. Label them A,B and C. Fill about half of bottle A with ordinary tap water. Fill bottle B with water which has been boiled for several minutes, to the same level as in A. In bottle C, take the same boiled water and of the amount as in other bottles. In each bottle put a few similar iron nails so that they are completely under water. Add a teaspoonful of cooking oil to the water in bottle C so it forms a film on its surface. Put the bottles away for a few days. Take out nails from each bottle and observe them. Explain your observations.

Prepare crystals of alum.