Most of Earth's mass of living organisms consists of which of the following elements?

• A. Carbon, hydrogen, oxygen, and nitrogen
• B. Iron, copper, zinc, and manganese
• C. Phosphorus, sulfur, chlorine, and fluorine
• D. Sodium, potassium, calcium, and magnesium

Answer: (A)

Verified step by step guidance

1. Understand the context: Living organisms are primarily composed of elements that are essential for building macromolecules such as proteins, carbohydrates, lipids, and nucleic acids. These elements are often referred to as 'biological elements' or 'CHON' elements.
2. Identify the key elements: Carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) are the primary elements that make up the majority of the mass in living organisms. These elements are involved in forming the backbone of organic molecules.
3. Compare the options: Evaluate each group of elements provided in the question. Iron, copper, zinc, and manganese are trace elements, meaning they are required in very small amounts. Phosphorus, sulfur, chlorine, and fluorine are important but do not constitute the majority of living mass. Sodium, potassium, calcium, and magnesium are involved in cellular processes but are not the primary mass contributors.
4. Relate to biological macromolecules: Carbon, hydrogen, oxygen, and nitrogen are integral to the structure of macromolecules like DNA, RNA, proteins, and carbohydrates, which are the building blocks of life.
5. Conclude: Based on the biological significance and abundance of these elements in living organisms, the correct answer is Carbon, hydrogen, oxygen, and nitrogen.