Which of the following is the constant of proportionality in Biot-Savart's Law?

Permittivity of free space Permeability of free space Permeability of free space/2π Permeability of free space/4π

Permeability of free space/4π

According to Biot-Savart's Law,  dB = \(\frac{μ_{o}}{4π}\) \(\frac{Idl Sinθ}{r^{2}}\) Constant of proportionality = \(\frac{μ_{o}}{4π}\)