15. Click in the vicinity of the symmetry element that has transformed L-Ala (left) into D-Ala (right).
Note: If you remember this image as an L-Ala coming out of the screen with its carboxyl group closest to you, the L- configuration of amino acid R-groups can be remembered as extending to your Left. And side-chains of D- amino acids extend (of course) to your right.
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Incorrect
The D- and L- enantiomorphs are related by reflection between the two images, i.e. the "symmetry element" is a mirror plane.