The cooking gas cylinder is filled with .......

Consider the following statements about Ramesh Chandra Dagar's work in the field of organic farming:
$I.$ Ramesh Chandra Dagar's work includes bee-keeping,dairy management,water harvesting,composting,and agriculture in a chain of processes.
$II.$ In this process,there is no need to use chemical fertilisers for crops as cattle excreta is used as manure.
$III.$ Crop waste is used for making compost,which is used as natural fertilizer.
$IV.$ Compost generates natural gas,which is used for the energy needs of the farm.
Which of the statements given above are correct?

How many of the following processes result in the release of $CO_2$ into the atmosphere? Burning of wood,forest fires,photosynthesis,combustion of fossil fuels,decomposition of organic matter,volcanic activity.

Which one of the following statements is $NOT$ correct?

Which is the main causative factor of desertification?

Which one of the following statements pertaining to pollutants is correct?