The correct option is (a) 1 only.
Explanation
The Earth's atmosphere is composed of a mixture of gases that are essential for life and various physical processes. Nitrogen is the primary constituent of the atmosphere, playing a crucial role in biological structures and atmospheric stability.
Statement-wise Analysis
- Statement 1 is Correct: Nitrogen is the most abundant gas in the Earth's atmosphere, constituting approximately 78% of the air by volume. Oxygen follows as the second most abundant gas at roughly 21%.
- Statement 2 is Incorrect: Nitrogen does not support combustion. Unlike oxygen, which is essential for burning, nitrogen acts as a diluent that moderates the intensity of combustion. If the atmosphere were comprised entirely of oxygen, fires would be uncontrollable.
- Statement 3 is Incorrect: Nitrogen is not toxic to all living organisms; on the contrary, it is an essential nutrient. It is a fundamental building block of amino acids, proteins, and nucleic acids (DNA and RNA), which are vital for all forms of life. While plants cannot utilize atmospheric nitrogen directly, they rely on nitrogen fixation to convert it into usable forms.
Key Takeaway
Nitrogen is the most abundant gas in the atmosphere (78%) and is chemically inert regarding combustion, serving as a vital structural component for life rather than a toxin.