A double convex lens has faces with 20 cm radii for each. The refractive index for glass is 1.5. It is immersed in carbon disulphide `(mu - 1.63).` It will act as
diverging lens of focal length 145 cm
diverging lens of focal length 125 cm
converging lens of focal length 125 cm
converging lens of focal length 20 cm