Question

Anaerobic bacteria digest animal waste and produce biogas [change A] . The biogas is then burnt as fuel [change B]. The following statement pertains to these changes . choose the correct one .
A.Process A is a chemical change
B.Process B is an chemical change
C.Both processes A and B are chemical change
D.None of these processes is a chemical change

Answer 1

Hint:Anaerobic bacteria are the bacteria which exists in an environment which has absence of oxygen.
-Burning or combustion of a substance is a type of chemical change as it is an irreversible process.

Complete step by step solution:
As we know anaerobic bacteria are bacteria that do not live or grow when oxygen is present in humans .and chemical change may be defined as the , when a chemical substances is transformed into one or more different substance , such as when iron being rust or displacement of zinc from zinc sulphate via copper .
Chemical change occurs or produces through a chemical reaction and the resulting substance has different properties from reactant because their atoms or molecules are differently arranged .
Some examples are , digestion of food , burning of paper , chemical battery usage , baking of cake etc .
Now , comes to the solution part in change A ,
Anaerobic bacteria digest animal waste and produce biogas that means a new product is formed that is biogas at the end of reaction .
$\text{animal waste}\left( {input} \right) \to biogas\left( {output} \right)$
From the above reaction , it is clear that change A is a chemical change .
In change B , biogas is then burnt as fuel that is energy is formed as a new product .
$fuel \to energy + ash$
New products are formed from old reactants , hence change B is also a chemical change .
The correct answer is option C.

Note:
-There are two types of changes: chemical changes and physical changes , Chemical change leads to the formation of a new identity whereas physical changes do not alter the identity of the molecules.
-Biogas is a household fuel, due to its high calorific value and since it is produced from waste, it is a form of sustainable energy.