The ability to fix atmospheric nitrogen is found in the

Leaves of some crop plants
Some marine red algae
Some blue-green algae
Cholera

The correct answer is C. Some blue-green algae.

Blue-green algae are a type of bacteria that are able to fix atmospheric nitrogen. This means that they are able to convert nitrogen gas from the atmosphere into ammonia, which is a form of nitrogen that plants can use. This is an important process because it helps to provide plants with the nitrogen they need to grow.

The other options are incorrect. Leaves of some crop plants do not have the ability to fix atmospheric nitrogen. Some marine red algae do have the ability to fix atmospheric nitrogen, but they are not as common as blue-green algae. Cholera is a disease that is caused by a bacteria called Vibrio cholerae. It is not related to the ability to fix atmospheric nitrogen.

Here is a more detailed explanation of each option:

  • Option A: Leaves of some crop plants. Leaves of some crop plants do not have the ability to fix atmospheric nitrogen. This is because they do not have the necessary enzymes to convert nitrogen gas into ammonia.
  • Option B: Some marine red algae. Some marine red algae do have the ability to fix atmospheric nitrogen. This is because they have the necessary enzymes to convert nitrogen gas into ammonia. However, they are not as common as blue-green algae.
  • Option C: Some blue-green algae. Some blue-green algae have the ability to fix atmospheric nitrogen. This is because they have the necessary enzymes to convert nitrogen gas into ammonia. They are the most common type of organism that can fix atmospheric nitrogen.
  • Option D: Cholera. Cholera is a disease that is caused by a bacteria called Vibrio cholerae. It is not related to the ability to fix atmospheric nitrogen.