А c) The vertical height of a tree is 18 m. The uppermost part
of the tree is broken by wind 5 m above the ground. At
what distance does the uppermost part of the tree touch
the ground from the foot of the tree?
B В​

Ifound the exercise on the internet. attached is the list mentioned above.in order for a compound to be considered optically active it can't have any axis or plan of symmetry. the molecule  shouldn't also  be superimposable on its mirror image.with such considerations, the compounds that are optically active are: -third compound on the first image is optically active; -second and third compound from the second image are optically actives.