When a lens of refractive index `n_(1)`, then the lens looks to be dissapeared only, if

A lens is made of flint glass (refractive index =1.5 ). When the lens is immersed in a liquid of refractive index 1.25 , the focal length:

A lens is made of flint glass (refractive index =1.5 ). When the lens is immersed in a liquid of refractive index 1.25 , the focal length:

A thin lens is made of glass of refractive index 1.6. Both the surfaces of lens are convex. When this lens is dipped in water of refractive index 4//3 then the lens will behave like

A biconvex lens of focal length f and radii of curvature of both the surface R is made of a material of refractive index n_(1) . This lens is placed in a liquid of refractive index n_(2) . Now this lens will behave like