The correct option is (a).
Explanation
The atmosphere is a gaseous envelope surrounding the Earth, held in place by the planet's gravitational pull. It is a crucial component of the environment that supports life by providing essential gases, regulating temperature, and shielding the surface from harmful solar radiation.
Statement-wise Analysis:
- Statement 1 is Correct: The atmosphere is described as a thin layer of air that surrounds the Earth. While it extends upwards for hundreds of kilometers, relative to the Earth's radius (approximately 6,371 km), it is a very thin protective layer.
- Statement 2 is Incorrect: The atmosphere extends far beyond 10 km. While the troposphere (the lowest layer) extends roughly up to 10–18 km depending on latitude, the entire atmosphere extends up to about 1,600 km above the surface. However, 99% of the total mass of the atmosphere is confined to the height of 32 km from the earth's surface.
- Statement 3 is Incorrect: The density of the atmosphere is not uniform. It is maximum at the sea level and decreases rapidly as we move up. Gravity pulls gas molecules toward the surface, compressing the air at lower altitudes, making it denser than the air at higher altitudes.
Key Takeaway:
The atmosphere is a vast gaseous layer extending hundreds of kilometers above the surface, characterized by a decrease in density and pressure with increasing altitude.