In the figure, an air lens of radii of curvature 10 cm (\[{{R}_{1}}\] = \[{{R}_{2}}\] = 10 cm) is cut in a cylinder of glass\[(\mu =1.5)\]. The focal length and the nature of the lens is [MP PET 1995; Pb. PET 2000]

• A.            15 cm, concave
• B.            15 cm, convex
• C.            \[\infty \], neither concave nor convex
• D.            0, concave