A: Population
If a group of one certain species are living in the same area they are a population. The same goes for humans, we are the same species and when we live in the same area we say we are part of a population. That’s why you would hear things like “the population of massachusetts is 2million” or whatever it is.
The answer is 300 joules of energy.
An energy pyramid is a presentation of the trophic levels in an ecosystem. Energy from the sun is transferred through the ecosystem by passing through various trophic levels. Roughly 10% of the energy is transferred from one trophic level to the next, thus preventing a large number of trophic levels.