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.

A change in which one or more new substances are formed is called a chemical change or a chemical reaction. It is an  irreversible change.

Here change A and change B both are chemical changes. Both reactions are irreversible and lead to the formation of new substances. There is also a change in the chemical properties of the reactants in both processes A and B.

$\mathrm{Animal} \mathrm{waste} \stackrel{\mathrm{anerobic} \mathrm{bacteria}}{\to } \mathrm{Bio} \mathrm{gas}\left({\mathrm{CH}}_4\right)$

$\mathrm{Bio} \mathrm{gas}\left({\mathrm{CH}}_4\right) \stackrel{\mathrm{burning}}{\to } {\mathrm{CO}}_2+\mathrm{other} \mathrm{substances}$

Hence, correct option is C.