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

(A) The order of arrangement of products according to their decreasing importance is:
$Penicillin > Biogas > Citric acid > Curd$
$1$. $Penicillin$ is the most important product for the welfare of human society. It is an antibiotic used for controlling various bacterial diseases,which has saved countless lives.
$2$. The second most important product is $Biogas$. It is an eco-friendly,renewable source of energy that helps in waste management and reduces dependence on fossil fuels.
$3$. The next important product is $Citric acid$,which is widely used as a food preservative and flavoring agent in the food industry.
$4$. The least important product is $Curd$,a nutritious food item obtained by the action of $Lactobacillus$ bacteria on milk,which is beneficial for digestion but less critical for global health or energy needs compared to the others.
Hence,the products in the decreasing order of their importance are: $Penicillin > Biogas > Citric acid > Curd$.