Which of the following is the source of energy for an ecosystem?

Energy flow in an ecosystem is.......

At which of the following levels is the energy the lowest?

Only a small amount of the energy stored in food is available to the next organism in a food chain because

Which of the following statements is not correct about energy flow in an ecosystem?

Assertion $A$: Heat energy is available for the functioning of a system.
Reason $R$: Some amount of energy is lost during energy transformation.
Which option is correct for Assertion $A$ and Reason $R$?