The correct option is (b).
Explanation
The origin of life on Earth is explained by the theory of chemical evolution (Chemotogeny). This theory suggests that the first forms of life arose from non-living organic molecules formed from simple inorganic constituents present in the primitive Earth's atmosphere.
Detailed Analysis:
- Essential Elements of Life: The vast majority of biological molecules (biomolecules) such as proteins, nucleic acids (DNA and RNA), carbohydrates, and lipids are constructed primarily from four elements: Carbon (C), Hydrogen (H), Oxygen (O), and Nitrogen (N). These are collectively known as the CHON elements and constitute approximately 96% of living matter.
- Primitive Atmosphere: According to the Oparin-Haldane hypothesis, the early Earth had a reducing atmosphere containing Methane ($CH_4$), Ammonia ($NH_3$), Water vapor ($H_2O$), and Hydrogen ($H_2$). These compounds provided the necessary Carbon, Hydrogen, and Nitrogen atoms to synthesize the first amino acids and simple sugars.
- Evaluation of Options:
- Option (a): Sodium is an electrolyte essential for cellular function but was not a primary structural element for the origin of organic molecules.
- Option (b): Carbon, Hydrogen, and Nitrogen are three of the four fundamental building blocks required to form the backbone of organic life (amino acids and nucleotides). This is the most appropriate set.
- Option (c) & (d): Calcium, Phosphorus, and Potassium are essential minerals (macronutrients) for structural and metabolic functions in evolved organisms, but they are secondary to C, H, and N regarding the primordial origin of organic matter.
Key Takeaway: The primary elements responsible for the formation of the first organic molecules and the origin of life are Carbon, Hydrogen, Oxygen, and Nitrogen (CHON).