The molecules or ions
that cannot be superimposed are
called chiral The two forms are called
dextro (d) and laevo (l) depending
upon the direction they rotate the
plane 
of 
polarised 
light 
in 
polarimeter (d rotates to the right, l toa
the left) Optical isomerism is common
in octahedral complexes involving
didentate ligands (Fig 5