Unity in Air Medium

In an air medium, the parameter that is unity is the relative permeability.

Explanation:

- Permittivity and permeability are fundamental parameters that describe the behavior of electromagnetic waves in a medium. Permittivity is associated with the response of a medium to an electric field, while permeability is associated with the response of a medium to a magnetic field.

- In the case of air, the permittivity is nearly equal to the permittivity of vacuum, which is denoted by ε0 and has a value of approximately 8.854 x 10^-12 F/m.

- On the other hand, the permeability of air is very close to the permeability of vacuum, denoted by μ0, which has a value of exactly 4π x 10^-7 H/m.

- The relative permittivity (εr) and relative permeability (μr) are dimensionless quantities that describe how a particular medium's permittivity and permeability compare to the permittivity and permeability of vacuum.

- In the case of air, the relative permittivity is very close to unity (εr ≈ 1), meaning that air's response to an electric field is almost the same as that of vacuum.

- Similarly, the relative permeability of air is also very close to unity (μr ≈ 1), indicating that air's response to a magnetic field is also almost the same as that of vacuum.

- Unity in relative permittivity and permeability means that the electric and magnetic fields in air propagate without significant distortion or interaction with the medium.

- This property makes air an excellent choice for many electrical and electronic applications, such as insulation, transmission of electromagnetic waves, and as a medium for capacitors and inductors.

Therefore, the correct answer is option C) Relative permeability.