Question

Animal dung is digested to produce biogas ( process A ) . The biogas is used in the stove as a fuel ( process B ) , which of the following is correct ?
A.Process A is a chemical change
B.Process B is a chemical change
C.Both A and B are chemical changes
D.Neither A nor B is a chemical change

Answer 1

A chemical change occurs when a new substance is formed during a chemical reaction that cannot be changed back into its original form , that is, the process is irreversible. For example, rusting of iron is a chemical change.

Complete step by step answer:
Biogas is a mixture of many gases such as methane $(C{H_4})$ , hydrogen sulphide $({H_2}S)$ and carbon dioxide $(C{O_2})$ .
Methanogens are a group of bacteria which grow anaerobically on cellulosic material and produce gases like methane $(C{H_4})$ carbon dioxide $(C{O_2})$ and hydrogen $({H_2})$ . One such bacterium is methanobacterium present in the gut of ruminants in which the bacteria helps in breakdown of cellulose.So the dung of cattle is used to produce biogas. It is produced in a biogas plant $10 - 15$ metres deep in which the wastes are collected .The plant has an outlet which supplies this biogas through a pipe to nearby houses ,especially in the rural areas .The spent slurry is removed and can be used as a fertiliser. Since, a new product is formed from organic compounds and it cannot be converted back into the original compounds, therefore, it is a chemical change.
The biogas produced is used as a fuel and is converted into different compounds which again cannot be reversed back into their original form therefore it is a chemical change.

So, the correct answer is Option C.

Note:
To check whether a chemical change has occured first the products are checked , If new products are formed it is a chemical reaction . Apart from this color , odor also changes, there is a change in temperature as well .