Solution:
When the refractive index of the liquid is the same as the lens material, no light will be reflected by the lens and hence it will not be visible. So, the lens immersed in a transparent liquid will not be visible.
A lens immersed in a transparent liquid is not visible. Under what condition can this happen?
When the refractive index of the liquid is the same as the lens material, no light will be reflected by the lens and hence it will not be visible. So, the lens immersed in a transparent liquid will not be visible.