$(+)$ $2-$Methylbutan$-1-$ol and $(-)$ $2-$Methylbutan$-1-$ol have different values for which property?

Allegra,a common prescription drug with the structure shown below,is given for the treatment of seasonal allergies. How many stereogenic carbon atoms does Allegra possess?

Solutions of optically active isomers rotate the plane of polarized light in a polarimeter. Match the following columns $(I)$ with $(II), (III)$,and $(IV)$ correctly:

$(I)$ Optical Activity	$(II)$ Form	$(III)$ Sign	$(IV)$ Rotation
$(A)$ Dextrorotatory	$d$	$(+)$	Right
$(B)$ Laevorotatory	$l$	$(-)$	Left
$(C)$ Optically Inactive (Racemic)	$dl$	$(\pm)$	Zero rotation

The optically active tartaric acid is named $D-(+)$ tartaric acid because it is related to $D-(+)$ glyceraldehyde in terms of:

Identify chiral and achiral molecules in each of the following pairs of compounds.

Which of the following is the erythro form and optically active?