Avalue two standards deviation from the mean is more likely to occur than a value three standard deviations from the mean.
a. true
b. false

This is True - A.

This is true because values which are less far apart from the mean; two standards deviations being closer than three standard deviations from the mean, are also more likely to occur. This is best illustrated when viewing a Gauss curve or a normal bell curve. 

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.