The question asks to identify the atmospheric layer responsible for reflecting radio waves, which is crucial for long-distance radio communication. We need to recall the characteristics and functions of different atmospheric layers.
C) Ionosphere — The Ionosphere is a region of the upper atmosphere, characterized by ionized gases, that reflects radio waves back to Earth, making long-distance radio communication possible.
The question asks to identify the outermost layer of the Earth's atmosphere that gradually transitions into outer space. This requires knowledge of the different layers of the atmosphere and their characteristics.
C) Exosphere is the outermost layer of the Earth's atmosphere that gradually merges into outer space. It extends from about 700 km to 10,000 km above the Earth's surface.
The question asks for the approximate normal lapse rate in the troposphere. The normal lapse rate refers to the average rate at which air temperature decreases with increasing altitude in the troposphere under normal atmospheric conditions.
A) 6.5°C per 1000 metres is the correct value for the normal lapse rate in the troposphere. This is a standard meteorological constant.
The question asks for the standard atmospheric pressure at mean sea level. This is a fundamental constant in meteorology and atmospheric science that candidates for competitive exams are expected to know.
C) 1013 millibars — This is the internationally recognized standard atmospheric pressure at mean sea level (specifically, 1013.25 mb, often rounded to 1013 mb).
The question asks to identify the atmospheric constituent that is most variable in amount and plays the most significant role in weather phenomena. We need to consider the properties and roles of each option in the atmosphere.
D) Water vapour — Water vapour is the most variable constituent of the atmosphere, with concentrations ranging from almost 0% to 4%. It is directly involved in the formation of clouds, precipitation (rain, snow, hail), and fog. It also plays a crucial role in the Earth's energy balance by absorbing and emitting infrared radiation, thus influencing temperature and driving weather patterns. Its phase changes (evaporation, condensation, freezing) release or absorb latent heat, which powers many atmospheric processes.
The question asks about the concentration of the atmosphere's total mass within the troposphere. To answer this, we need to recall the general characteristics and composition of the Earth's atmospheric layers, specifically how atmospheric density and mass distribution change with altitude.
D) About 75-80 per cent is the correct answer. The troposphere, being the lowest and densest layer of the atmosphere, contains roughly 75% to 80% of the total atmospheric mass. This is a well-established fact in atmospheric science.