The dimensional formula of coefficient of viscosity is

$[MLT^{-1}]$ $[M^{-1}L^2T^{-2}]$ $[ML^{-1}T^{-1}]$ none of these

$[ML^{-1}T^{-1}]$

F = 6$\pi\eta$ vr $[\eta]=\frac{[F]}{[vr]}=\frac{[MLT^{-2}]}{[LT^{-1}][L]}=[ML^{-1}T^{-1}]$