A small ball of mass \( m \) and density \( \rho \) is dropped in a viscous liquid of density \( \rho_{0} \). After sometime, the ball falls with constant velocity. The viscous force on the ball is:
\( mg \left( 1 + \dfrac{\rho}{\rho_{0}} \right) \)
\( mg \left( \dfrac{\rho_{0}}{\rho} - 1 \right) \)
\( mg \left( 1 - \dfrac{\rho_{0}}{\rho} \right) \)
\( mg \left( 1 - \rho \rho_{0} \right) \)