The ratio C_p/C_v for noble gases is

The ratio of specific heats (Cp/Cv) for noble gases depends on their atomic and molecular structure.

For monoatomic gases, such as the noble gases He, Ne, Ar, Kr, and Xe, the ratio of specific heats is constant and is equal to 5/3 or approximately 1.67. This is because the atoms of these gases have only three degrees of freedom of movement (translational motion in the x, y, and z directions), and no rotational or vibrational degrees of freedom.

For diatomic gases, such as H2, N2, O2, and F2, the ratio of specific heats is also constant but is equal to 7/5 or approximately 1.4. This is because in addition to the three translational degrees of freedom, diatomic molecules also have two rotational degrees of freedom.

For other gases and mixtures of gases, the ratio of specific heats can vary depending on the complexity of the molecular structure and the degree of freedom of their constituent atoms and molecules.

So, for noble gases such as He, Ne, Ar, Kr, and Xe, the ratio of specific heats (Cp/Cv) is 5/3 or approximately 1.67.