The number of optical isomers possible for the given organic molecule is? $\ce{CH_3-C^*H(OH)-CHCl-CH_2Cl}$ (the configuration is fixed at $\ce{C^*}$)
The given answer is 2. The carbon marked with an asterisk is chiral, and the carbon to the right of it is also chiral. Doesn't that give 4 isomers? What does "configuration is fixed" mean?