Earth Science

A planet retains its atmosphere when its gravity is strong enough to hold the atmospheric gases and when the temperature is low enough to prevent the gases from escaping into space. High temperature increases gas velocity, making it easier for gases to escape, while strong gravity helps retain them.

The mesosphere extends approximately from 46 km to 85 km above Earth's surface. This range is widely accepted in atmospheric science, making option A the most accurate choice.

The troposphere contains about 75–80% of the atmosphere's mass because it is the lowest layer where most of the air molecules are concentrated due to gravity. This makes it the densest atmospheric layer compared to the stratosphere, mesosphere, and thermosphere.

The troposphere is the lowest layer of Earth's atmosphere where almost all weather phenomena occur, including clouds, rain, and storms. Other layers like the stratosphere, mesosphere, and thermosphere do not have weather.

The age of the solar system is widely accepted by scientists to be about 4.5 billion years, based on radiometric dating of meteorites and Earth rocks. This makes option C the correct choice.

The elastic rebound theory explains the causes of earthquakes by describing how stress builds up in rocks until they suddenly break and release energy, causing an earthquake.

Earthquake waves travel faster in solid, rigid materials like rock because these materials transmit seismic energy more efficiently than fluids or loose materials. Among the options, 'Flexible rock' (corrected spelling) is the best choice as waves travel slower in water, air, or soil.

Weather and climate are primarily driven by solar radiation, which provides the energy that powers atmospheric processes. Earth's internal heat and gravity have minimal direct impact on weather and climate patterns.

The troposphere is the lowest layer of Earth's atmosphere where all weather occurs and where humans breathe. The other options are either incorrect atmospheric layers or unrelated terms.

Volcanoes commonly occur at divergent plate boundaries where plates move apart, convergent plate boundaries where plates collide, and at hotspots which are volcanic regions fed by underlying mantle plumes. Therefore, all these locations are typical for volcano formation.