Question

2,4-pentanediol : has it two meso compounds (i.e. 2 pairs of identical isomers) ?

Answer 1

From wikipedia, "For example, in 2,4-pentanediol, both the second and fourth carbons, which are stereocenters, have all four substituents in common."
http://en.wikipedia.org/wiki/Meso_compound

Here is a diagram of chemical structure:
http://www.rdchemicals.com/chemicals.php?mode=details&mol_id=2482