According to 10% law, the energy available to each successive trophic level is 10% of the previous trophic level.
Given, energy available at the third trophic level = 50 KJ
Energy available at second trophic level = 50 KJ x 10 = 500 KJ
Therefore, energy available at the producer level (first trophic level) = 500 KJ x 10 = 5000 KJ

Explanation:

In a food chain, energy is transferred from one trophic level to another. The amount of energy available at each trophic level decreases as we move up the food chain. This is due to the inefficiency of energy transfer and the fact that energy is lost as heat during metabolic processes.

Given:
Energy available at the third trophic level = 50 KJ

Calculating the energy available at the producer level:

The producer level is the first trophic level in a food chain. It consists of autotrophic organisms such as plants that convert sunlight into chemical energy through photosynthesis. This energy is then passed on to the consumers in higher trophic levels.

To find the energy available at the producer level, we need to determine the energy loss at each trophic level. The energy transfer efficiency between trophic levels can vary, but a commonly used estimate is about 10% efficiency.

So, the energy available at each trophic level can be calculated using the formula:

Energy available at a trophic level = Energy available at the previous trophic level * Energy transfer efficiency

Since the given energy is at the third trophic level, we can calculate the energy available at the producer level by reversing the energy transfer equation:

Energy available at the producer level = Energy available at the third trophic level / (Energy transfer efficiency) ^ (Number of trophic levels)

In this case, the number of trophic levels from the third trophic level to the producer level is 3 (including the third trophic level).

Energy available at the producer level = 50 KJ / (0.10) ^ 3

Calculating the value:

Energy available at the producer level = 50 KJ / 0.001

Energy available at the producer level = 50,000 KJ

Therefore, the energy available at the producer level is 50,000 KJ, which can be represented as option 'C' in the given answer choices.