ANS:A - compressibility

At equal reduced conditions, i.e., at corresponding states, the compressibility of different gases is nearly the same. This concept is fundamental in the study of the behavior of gases, particularly when comparing different gases under similar conditions. By using reduced pressure and reduced temperature, which are normalized values, we can compare gases' behavior regardless of their individual molecular weights or other properties. Therefore, the correct answer is: (a) compressibility Compressibility refers to the extent to which a substance can be compressed or squeezed under the application of pressure. In the context of gases, compressibility is a measure of how much the volume of a gas decreases in response to an increase in pressure, or conversely, how much it increases in volume when pressure is reduced. When substances are at equal reduced pressure and equal reduced temperature, they are said to be in corresponding states. In this state, gases exhibit similar behavior regardless of their individual molecular weights or other properties. Now, why is compressibility significant in corresponding states?

1. Standardization of Comparison: Compressibility provides a standardized measure for comparing gases' behavior under similar conditions. By comparing compressibility at corresponding states, we can assess how gases respond to changes in pressure in a uniform manner.
2. Ideal Gas Behavior: According to the ideal gas law, at low pressures and high temperatures, gases behave ideally, meaning their behavior is described accurately by the ideal gas equation 𝑃𝑉=𝑛𝑅𝑇PV=nRT, where 𝑃P is pressure, 𝑉V is volume, 𝑛n is the number of moles of gas, 𝑅R is the gas constant, and 𝑇T is temperature. Under corresponding states, gases tend to behave more ideally, and their compressibility approaches that of an ideal gas.
3. Universal Behavior: While individual gases may have different molecular weights and other properties, at corresponding states, they exhibit similar responses to changes in pressure due to their similar reduced conditions. This suggests a universal behavior among gases under these standardized conditions.