Q.Describe the composition of atmosphere.

The atmosphere is a layered blanket of gases held around the Earth by gravity, and its composition is not uniform—it changes with altitude. Near the surface, the air is a mechanical mixture of gases, with nitrogen and oxygen dominating almost everything else.

• Nitrogen (about 78%) — the most abundant gas, largely inert, dilutes oxygen and is essential for proteins through the nitrogen cycle.
• Oxygen (about 21%) — the second most abundant, vital for respiration and combustion.
• Argon (about 0.9%) — a noble gas, chemically unreactive.
• Carbon dioxide (about 0.03–0.04%) — present in trace amounts, but crucial for photosynthesis and as a greenhouse gas that traps heat.
• Other gases — neon, helium, methane, ozone, and hydrogen occur in extremely small traces. …

Think of the atmosphere not as empty space but as a thin, invisible ocean of air wrapped around the Earth. It is held in place by gravity, and its composition is remarkably stable in the lower layers — a careful balance that makes life possible. If you took a hundred breaths of this air, about seventy-eight of them would be nitrogen, twenty-one would be oxygen, and the remaining one would be a mix of everything else. That single percent, small as it sounds, holds the key to weather, climate, and the very chemistry of living things.

Nitrogen dominates the mix, making up roughly 78 percent of the atmosphere by volume. It is largely inert, meaning it does not easily react with other substances, which is why it acts as a stable filler that dilutes oxygen and keeps combustion from being too rapid. Oxygen, at about 21 percent, is the life-giving component — essential for respiration in animals and for burning fuels. Together, these two gases account for nearly 99 percent of the dry air around us.

The remaining one percent is a fascinating assortment. Argon, a noble gas, takes up almost all of that leftover share, sitting at just under one percent. Carbon dioxide, though present in only trace amounts — roughly 0.03 to 0.04 percent — punches far above its weight. It absorbs heat radiated from the Earth's surface, creating the greenhouse effect that keeps the planet warm enough for life. It is also the raw material for photosynthesis, so plants draw it in and release oxygen, completing a cycle that sustains the entire biosphere.

Water vapour is the great variable. Unlike the fixed gases, its amount changes from place to place and moment to moment — from nearly zero over deserts to about four percent in humid tropical air. It is the engine of weather: it forms clouds, brings rain, and stores enormous amounts of latent heat. Alongside water vapour, the atmosphere carries tiny solid particles — dust, pollen, smoke, and sea salt — collectively called aerosols. These particles are not just pollution; they serve as condensation nuclei, the tiny surfaces on which water droplets form to create clouds and precipitation. …