Which of the following two are the major constituent of Bio-gas ?1.Methane2.Butane3.Carbon dioxide4.Carbon monoxideSelect the correct answer from the code given below:

1. A

   1 and 3

   1 and 3. Biogas is mostly methane (about 50–75%) plus carbon dioxide. Butane and CO are not the two majors.

2. B

   3 and 4

   3 and 4. CO2 is present; CO is not a major constituent.

3. C

   2 and 3

   2 and 3. Butane is LPG, not biogas.

4. D

   1 and 2

   1 and 2. Methane yes; butane no.

Summary. Official key is (a) 1 and 3. Major biogas pair: methane and carbon dioxide. Also note: CH4 share — Typically 50–75% of biogas; CO2 share — Typically 25–50%; LPG — Propane + butane; not this mix; Gobar gas — Cattle-dung anaerobic digester.