How much energy is available at each level if the krill (on trophic level 3) ends up with 450 kcal of energy?​

The amount of energy at each trophic level decreases as it moves through an ecosystem. As little as 10 percent of the energy at any trophic level is transferred to the next level; the rest is lost largely through metabolic processes as heat. If a grassland ecosystem has 10,000 kilocalories (kcal) of energy concentrated in vegetation, only about 1,000 kcal will be transferred to primary consumers, and very little (only 10 kcal) will make it to the tertiary level. Energy pyramids such as this help to explain the trophic structure of an ecosystem: the number of consumer trophic levels that can be supported is dependent on the size and energy richness of the producer level.

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.

maybe because its impossible for balloons to lift a whole entire house.