In an ecosystem where 500,000 kcal of sunlight is available for producers, approximately how much chemical energy will be contained in secondary consumers?

The answer is 50 kcal by the formula of 10% - 500kcal x .1 = 50 kcal it is the approximately chemical energy that can contain by the secondary consumers.
1%- 500,000 kcal x .01 = 5,000 kcal for producers. 
10%- 5,000 kcal x .1 = 500 kcal for primary consumers.  
10%- 500 kcal x .1 = 50 kcal for secondary consumers.
10%- 50 kcal x .1 = 5 kcal for tertiary consumers.
Each trophic level receives less and less energy, so fewer organisms can be supported at higher levels.
10% of energy gets passed to next level in form of chemical bonds and 1 decimal place.

The answer is c. valence electrons