At constant temperature, in a given mass of an ideal gas, the product of pressure and volume always remains constant. This observation is known as Boyle's law, which states that the pressure of a given amount of gas is inversely proportional to its volume, as long as the temperature and amount of gas remain constant.

Explanation:
Boyle's Law is based on the behavior of gases when subjected to changes in pressure and volume while keeping the temperature constant. To understand why the product of pressure and volume remains constant in this scenario, let's break down the concept further.

1. Boyle's Law:
- Boyle's Law states that for a given mass of gas at constant temperature, the product of pressure and volume is constant.
- Mathematically, it can be represented as P₁V₁ = P₂V₂, where P₁ and V₁ are the initial pressure and volume, and P₂ and V₂ are the final pressure and volume.

2. Inverse Proportionality:
- Boyle's Law describes an inverse relationship between pressure and volume.
- As the volume of a gas decreases, the gas particles become more confined, leading to more frequent collisions with the container walls, resulting in an increased pressure.
- Conversely, as the volume of a gas increases, the gas particles have more space to move around, causing fewer collisions with the container walls, resulting in a decreased pressure.

3. Constant Temperature:
- The constant temperature condition in Boyle's Law ensures that the average kinetic energy of the gas particles remains constant.
- When the temperature is constant, the gas particles' speed and energy distribution do not change.
- Therefore, the pressure and volume changes observed in Boyle's Law are solely due to the change in the space available to the gas particles.

4. Implications:
- As the gas volume decreases, the pressure increases to maintain the constant product of pressure and volume.
- Similarly, as the gas volume increases, the pressure decreases to maintain the constant product.
- This behavior can be observed in various practical applications, such as the compression and expansion of gases in engines, refrigerators, and other devices.

In conclusion, at constant temperature, the product of pressure and volume of an ideal gas remains constant according to Boyle's Law. This relationship between pressure and volume provides insights into the behavior of gases under different conditions and is crucial in understanding their properties and applications.