Arrange the following in the decreasing order (most important first) of their importance, for the welfare of human society. Give reasons for your answer.

Biogas, Citric acid, Penicillin and Curd

The importance of substances in decreasing order is

Pencillin, Biogas, Curd and Citric acid

Pencillin is an important antibiotic which helps in fighting against various bactaria; infections , hence , it is important for human welfare. Biogas is an eco friendly source of energy and helps in curbing pollution. Curd is a souce of Vitamin B12 and it has several benefits as food. Citric acid is used as a preservative in food industry.