Biogas primarily consists of .......

Gobar gas contains mainly

Which of the following gases is primarily produced by the action of anaerobic bacteria on sewage?

Identify the odd one out in the context of biogas composition.

$A$: Biogas is a mixture of various gases.
$R$: The type of gases produced depends on the microbes and the organic substrate used.

Mohan was writing a report on the benefits of biogas:
$i$. It is cheap and safe
$ii$. Can be used for cooking
$iii$. Can be transported easily
$iv$. Causes pollution
Which one of the above statements has been reported incorrectly?