How to check which compound will show optical isomerism?
In the first image due to the absence of any chiral carbon or steriogenic centre it does not show optical activity.
In the second image there is a plane of symmetry thus it ceases to be optically active(the plane of symmetry is perpendicular to the substituted butane ring).finally Alenes are optically active as the successive π orbitals lie on a different plane.You can definitely get the structure of alene from a reference book and the due to successive π bonds they lie on a different plane (the π orbitals).thus they are optically active.
Thus in compounds where there are no chiral centre check centre of symmetry,axis of symmetry and plane of symmetry as a CHIRAL carbon is essentially an unsymmetrical molecule.Hope you understood:).