Given that chemical changes is a form of change of matters that deal with the combination of various substances to form a new substance entirely that has different chemical and physical characteristics from its parents' substances.
Hence, when Animal waste is acted upon by anaerobic bacteria to produce biogas it is considered a chemical change.
Similarly, when biogas burnt as fuel it is also considered as a chemical change.
Therefore, in this case, the correct answer is "Both Change A and B" are chemical changes.
chemistry is basically the study of matter and their properties. it also it also explains how and why some substances combine or separate to form different substances.
