Which of the following molecules can NOT be isolated as an optically pure sample?

W) Valine [VAL-een]

X) Tartaric acid

Y) Epichlorohydrin [ep-i-kawr-uh-HY-drin]

Z) Trans-4-chlorocyclohexanol [klohr-oh-SY-kloh-HEK-suh-nol]
Z) TRANS-4-CHLOROCYCLOHEXANOL