(a) :Herbivores are eaten by primary carnivores. Only $10\%$ of the herbivores productivity is utilized for raising productivity of primary carnivores. The rest is consumed in ingestion, respiration, maintenance of body heat and other activities. Higher carnivores similarly are able to retain only $10\%$ of energy present in primary carnivores. It is called $10\% $ law which was proposed by Lindemann. Accordingly, if plant trapped $20\ J$ of energy, mice will have $2\ J$, snake will have $0.2\ J$ and hence, peacock will have $0.02\ J$ of energy.