Biology

Step 1: Analyze statement A.
The most abundant elements in living organisms are Oxygen, Carbon, Hydrogen, and Nitrogen. It is a key component, making this statement correct.

Step 2: Analyze statement B.
Breaking the strong triple bond in atmospheric nitrogen (N ) is an extremely energy-intensive process. Both the industrial Haber-Bosch process and biological nitrogen fixation by bacteria require massive energy inputs. This statement is correct.

Step 3: Analyze statement C.
Nitrogen is a fundamental component of all amino acids, which are the building blocks of proteins. It is also a component of the nitrogenous bases in nucleic acids (DNA and RNA), as well as in other molecules like ATP and chlorophyll. The statement that it is only found in nucleic acids is incorrect.

Step 4: Analyze statement D.
The Earth's atmosphere is approximately 78% nitrogen gas (N ). The triple bond in N makes it very stable and chemically inert, so it is not readily available for use by most organisms. This statement is correct. Conclusion: Statement C is the incorrect one.

Step 1: Analyze statement A.
A coral reef is made of vast colonies of tiny animals called coral polyps. A single polyp is an invertebrate animal, typically only a few millimeters in diameter. Statement A is correct.

Step 2: Analyze statement B.
Corals have a narrow range of environmental tolerances. Increased ocean temperature (heat stress) and decreased pH (ocean acidification) are major stressors that can disrupt their symbiotic relationship with algae and lead to coral bleaching. Statement B is correct.

Step 3: Analyze statement C.
Corals live in a symbiotic relationship with microscopic algae called zooxanthellae. The coral polyp provides the algae with a protected environment and the compounds they need for photosynthesis (CO and nutrients like nitrates and phosphates). Statement C is correct.

Step 4: Analyze statement D.
Coral bleaching is the process where corals expel the symbiotic algae living in their tissues, causing them to turn completely white. This is a stress response, primarily to heat, not a mechanism to get rid of pathogens. The loss of the algae can lead to the coral's death. Statement D is incorrect. Conclusion: Statements A, B, and C are correct.