Right answer is (c) \(K_B=\frac{3}{2π} \left[\frac{1}{1+(\frac{r}{z})^2} \right]^{\frac{5}{2}}\)
Easy explanation: The Boussinesq influence factor is given by,
\(K_B=\frac{3}{2π} \left[\frac{1}{1+(\frac{r}{z})^2} \right]^{\frac{5}{2}}\) where the KB= Boussinesq influence factor which is a function of r/z ratio which is a dimensionless factor.