If CO${}_2$ is removed totally from the biosphere, which organism will be affected first?

The correct option is C Producers
Producers are photosynthetic organisms that synthesize their own food in presence of sunlight. They convert solar energy into chemical energy. The carbon dioxide and water in the atmosphere are converted into oxygen and glucose molecule in sunlight. Hence, if carbon dioxide is removed completely from the biosphere, producers will be affected first as they cannot synthesize their food.

Thus, the correct answer is 'Producers.'