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.

Production of biogas from animal waste by the action of bacteria is chemical change because new substance biogas is formed. Thus, process A is a chemical change. Biogas works as fuel and produces heat. Hence, process B is also a chemical change.