What is the equation derived from Gay-Lussac's Law?

The equation derived from Gay-Lussac's Law is represented by the relationship between pressure and temperature of a gas when the volume is kept constant. This law states that the pressure of a gas is directly proportional to its absolute temperature. The correct representation of this relationship is given by the equation where the product of the initial pressure and the final temperature equals the product of the final pressure and the initial temperature.

This formulation shows that if the temperature of a gas increases, its pressure must also increase, provided the volume remains unchanged. This key principle is essential for understanding how gases behave in various conditions, particularly in high-altitude flight scenarios where temperature and pressure can significantly affect performance and safety.

The other options do not accurately reflect the direct proportionality defined by Gay-Lussac's Law. Instead, they either misrepresent the relationship between pressure and temperature or introduce operations (addition or subtraction) that don’t apply to this law. Thus, the correct answer illustrates the fundamental concept of gas behavior in thermodynamics as it relates to pressure and temperature changes.