Question

concave & convex lens of same mass &radii rotate about an axis passing through their centre &perpendicular to the plane which one will have greater mnment of inertia

Answer 1

Well, moment of inertia is something like MR². (There are a few proportionality constants depending on the actual shape)

Concave lenses have more of their mass concentrated on the outer radius. So they should have a higher moment of inertia