The main idea is that the atmosphere is dominated by two gases, with all the rest making up only a small amount. By volume, nitrogen about 78% and oxygen about 21% leave roughly 1% for every other gas combined. That means trace gases such as argon, carbon dioxide, neon, helium, methane, krypton, hydrogen, and others together contribute about one percent of the air. CO2 itself is only around 0.04% and the rest of the trace gases add up to roughly the remaining small fraction, giving a total near one percent. The other options would imply a much larger or smaller share for all those minor gases, which doesn’t align with how the atmosphere is actually composed.

Weight of fuel is found by multiplying its density by the volume. A gallon is a unit of volume, and aviation fuels have densities such that a rough rule of thumb is about 6 pounds per gallon. This convenient figure is widely used for quick planning and maintenance calculations, even though the exact weight can vary with fuel type (Jet fuel versus AVGAS) and temperature. In practice, Jet A is slightly heavier (around 6.7 pounds per gallon at standard conditions) and AVGAS is in a similar range, but for rough estimates the six-pound figure is the common, widely taught approximation. So the choice matching that practical value best represents the typical weight of one gallon of average aviation fuel.

Heat transfer moves energy from hotter to cooler areas through three main mechanisms: conduction, where energy transfers through direct contact within or between solids; convection, where moving fluids carry heat with their bulk motion; and radiation, where energy travels as electromagnetic waves without needing a medium. Evaporation is a phase-change process that requires latent heat and can cause cooling, but it is not a separate mechanism by which heat moves. It can occur because heat is added to a liquid, driving it to vapor, yet the primary modes of transferring heat are conduction, convection, and radiation. Therefore, evaporation is not considered a method of heat transfer.

Corrosion on aluminum airframes shows up as surface changes and material loss caused by chemical or electrochemical attack. The typical signs are pitting, which are small pits where the metal has been eaten away; discoloration, which comes from oxide or other corrosion products changing the metal’s color; and coating failure, where the protective paint or primer breaks down and lets corrosion proceed underneath. Warpage of the skin isn’t a typical corrosion sign because distortion or bending of the skin points to structural deformation from other causes, such as mechanical damage, improper manufacturing processes, or thermal/loads effects. While corrosion can eventually weaken a structure, its common visual indicators aren’t warped skin; they’re pits, color changes, and coating problems.