The correct option is 1 and 3 only.
Explanation
Carbon is a versatile element that forms the basis of all living organisms and is found in various forms in the non-living world, though its elemental abundance varies significantly across different spheres.
Statement-wise Analysis:
- Statement 1 is Correct: The Earth's crust contains a very minute amount of carbon, approximately 0.02%. It exists primarily in the form of minerals such as carbonates, hydrogen carbonates, coal, and petroleum.
- Statement 2 is Incorrect: The atmosphere contains approximately 0.03% carbon dioxide by volume. The figure of 21% refers to the approximate volume of Oxygen in the atmosphere.
- Statement 3 is Correct: Carbon is a fundamental constituent of all living systems. It forms the structural backbone of essential biomolecules, including proteins, carbohydrates, fats, and nucleic acids.
Key Takeaway: While carbon is the central element of life (organic chemistry), its concentration in the Earth's crust (0.02%) and atmosphere (0.03%) is extremely low compared to elements like Oxygen (21% in atmosphere) or Nitrogen (78% in atmosphere).