Energy transfer from one trophic level to another in a food chain is: (in $\%$)

Identify the missing link in the following food chain:
Plants $\to$ Insect $\to$ Frog $\to$ $A$ $\to$ Hawk.

The concept of the food chain was introduced by which of the following ecologists?

In an ecosystem,$1000 \ J$ of energy is stored at the producer level. How much energy will be available at the secondary consumer level (in $J$)?

Which one of the following components of an ecosystem comes from outside?

The second order consumer in a food chain is