Which gases are present in biogas?
$(i)$ Methane
$(ii)$ Hydrogen sulfide
$(iii)$ Carbon dioxide
$(iv)$ Carbon monoxide
$(v)$ Butane
$(vi)$ Ethane

$A$ - The excreta (dung) of cattle is rich in methanogen bacteria.
$R$ - Thus,dung can be used in biogas production.

Consider the following statements about methanogenic bacteria:
$I.$ Methanogenic bacteria are commonly found in the anaerobic sludge formed during sewage treatment.
$II.$ These bacteria also occur in the rumen of cattle,where they act upon cellulosic material to break down cellulose.
$III.$ They play a very important role in the nutrition of cattle by digesting cellulosic material.
Which of the statements given above are correct?

Ruminant animals can digest cellulose in their food,whereas human beings are unable to do so. This is because

Which of the following gases is useful as an energy fuel?

Statement $X$: Biogas is used as a fuel for energy.
Statement $Y$: Biogas contains $H_2S$,$CO_2$,and oxygen gas.