Understanding Main Ideas
28 What are the two main differences between Pluto and the gas giants?
29 Why doesn't the gas on a gas giant escape into space, as it has on
Mercury?
30 What object in the solar system has a composition similar to that of the gas
giants?

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.