Layers of the atmosphere

Correct answer: B. Its height can vary with latitude, season, and atmospheric conditions

The correct answer is B. The tropopause is a transition region, not a fixed level. Its height varies with latitude, season, and atmospheric conditions; it is generally higher in the tropics and lower toward the poles. The other options give incorrect locations or describe it as fixed.

Correct answer: C. Temperature reaching a minimum at the mesopause and increasing above it

The correct answer is C. The mesopause marks the upper boundary of the mesosphere and is a region of very low atmospheric temperature. Above it, temperature increases with altitude in the thermosphere as its sparse gases absorb energetic solar radiation. Rainfall and sea breezes are not clues to this boundary.

Correct answer: C. Thermosphere

The correct answer is C, the thermosphere. Solar radiation gives its gas particles high average kinetic energy, corresponding to a high temperature. But the air is extremely thin, so there are very few particles to transfer energy to a person or object; the sensation of heat can therefore remain weak.

Correct answer: A. The troposphere is a layer in the thermal classification, and the homosphere is the region where gases are relatively well mixed

A is correct. Thermal layers are distinguished by how temperature changes with altitude, and the troposphere is one such layer. Structural classification concerns how atmospheric gases are distributed: gases are relatively well mixed in the homosphere, while their composition varies more with altitude in the heterosphere.

Correct answer: A. The exobase is the lower boundary of the exosphere; above it, collisions between particles are very infrequent

A is correct. The exobase marks the lower boundary of the exosphere. Above it, the atmosphere is so thin that particle collisions are very infrequent and particles can travel long distances between collisions. It is not a boundary of the troposphere or a region of ozone maximum.

Correct answer: A. Thermosphere

A is correct. Increased solar ultraviolet and extreme-ultraviolet energy can heat and expand the thermosphere, raising atmospheric density at some satellite altitudes. The resulting increase in drag can affect low-Earth-orbit satellites. The air there remains far less dense than air near Earth’s surface.

Correct answer: B. Troposphere, stratosphere, mesosphere, thermosphere

Option B is correct. In the troposphere, temperature generally decreases with height; in the stratosphere it increases, largely because ozone absorbs ultraviolet radiation. It decreases again in the mesosphere and increases in the thermosphere. Therefore, the stated decrease–increase–decrease–increase pattern identifies the sequence troposphere, stratosphere, mesosphere, thermosphere.

Correct answer: C. Stratosphere

Option C is correct. The stratosphere is comparatively stable, so it has less vigorous vertical mixing than the troposphere, where most ordinary weather occurs. Stratospheric ozone absorbs much of the Sun’s ultraviolet radiation, making radiation absorption and ozone chemistry important there.