Explanation:

In a food chain, the largest population is that of producers. Producers are organisms that can synthesize their own food using sunlight, water, and carbon dioxide through the process of photosynthesis. They are typically plants, algae, and some types of bacteria.

Reasons why producers have the largest population:

1. Energy Source: Producers are at the lowest trophic level in a food chain and serve as the primary source of energy. They convert solar energy into chemical energy, which is stored in the form of carbohydrates. This energy is then transferred to higher trophic levels.

2. Abundance: Producers have the advantage of being able to reproduce rapidly and in large numbers. They can cover vast areas, such as forests, grasslands, and oceans. This abundance provides a substantial food source for other organisms.

3. Food Availability: Producers provide food for all other organisms within the food chain. They form the base of the food chain and support the growth and survival of primary consumers, secondary consumers, and even decomposers.

4. Efficiency of Energy Transfer: As energy moves up the food chain, it becomes less efficient. Only a fraction of the energy consumed by one trophic level is transferred to the next trophic level. This limits the population sizes of organisms at higher trophic levels. Producers, being at the bottom of the food chain, have access to the maximum amount of energy available.

5. Ecological Niche: Producers occupy a specific ecological niche and are well-adapted to their environment. They have a wide range of species diversity, which further contributes to their population size.

Conclusion:

In summary, producers have the largest population in a food chain due to their ability to convert solar energy into chemical energy, their abundance, their role as a primary food source, the efficiency of energy transfer, and their ecological niche. They form the foundation of the food chain and support the existence of all other organisms within it.