Identify the organism from the following that receives the least amount of energy and is considered ecologically weak?

The main source of energy in an ecosystem is .........

If the primary producers have $100 \ J$ of energy,how much energy does the secondary consumer receive (in $J$)?

If $20 \ J$ of energy is trapped at the producer level,then how much energy will be available to the peacock as food in the following food chain (in $J$)?
Plant $\rightarrow$ Mice $\rightarrow$ Snake $\rightarrow$ Peacock

The ultimate energy source of the ecosystem is

The best source of energy in the environment is