In a biogas plant,when does the gas holder (cover) rise?

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?

The production of biogas in India is largely due to the efforts of .......

Statement $P$: Bacteria produce methane gas due to metabolic processes like anaerobic respiration.
Statement $Q$: Bacteria act on starchy materials.

Assertion $(S)$: $H_2$ is capable of converting solar energy into chemical energy.
Reason $(R)$: Photosynthetic microorganisms produce $H_2$.

What is the main component of gobar gas (biogas)?