The answer to this question with the options presented in the problem would be A. 50.
It is said by experts that in the energy pyramid, 90% of energy is lost for life processes such as photosynthesis, respiration, and the like. So this means that only 10% will remain for the consumer to have. That would be saying that if suppose there are 500 units of energy available at the producer level of the energy pyramid, to get the units of energy available to the first-level consumer is to have the 10% of 500 which is 50.
