Which of the following are meso compounds?

A meso compound has stereocentres related by an internal mirror plane, which needs a symmetric constitution and opposite descriptors. The butane-1,4-diol and the pentane-2,4-diyl compound are symmetric and (R,S), so both are meso. 2,3-Dichloropentane is unsymmetrical (methyl versus ethyl ends) and therefore chiral. (1R,3R)-1,3-dimethylcyclohexane is the trans isomer, which is chiral; the cis isomer is (1R,3S).