Correct Option
The correct option is Sulphuric acid.
Explanation
The atmosphere of Venus is extremely dense and hot, serving as the classic example of a "runaway greenhouse effect." While the gaseous atmosphere is dominated by Carbon Dioxide ($CO_2$), the planet is shrouded in thick, opaque clouds that determine its visual appearance and albedo (reflectivity).
Detailed Analysis
- Composition of Clouds: The thick, yellowish clouds covering Venus are primarily composed of droplets of concentrated Sulphuric Acid ($H_2SO_4$). These clouds are formed by photochemical reactions between Sulphur Dioxide ($SO_2$) and water vapor in the upper atmosphere.
- Role in Atmosphere: These clouds reflect approximately 75% of the sunlight that falls on them, making Venus the brightest planet in the sky. However, they also contribute to the thermal blanket that traps heat on the surface.
- Comparison with Earth: While Sulphuric Acid is a component of acid rain on Earth (a form of environmental pollution), on Venus, it forms a permanent, global cloud layer.
Key Takeaway: The primary gas in Venus's atmosphere is Carbon Dioxide (causing the greenhouse effect), but the thick clouds are composed of Sulphuric Acid.