Is (2R,3S)-2,3-dichloropentane optically inactive?
To have an optically inactive meso compound with two chiral centers:

1)  the chiral centers must have opposite configuration

2)  the chiral centers must have the same set of fragments bonded to them

Among other things the 2 carbon has a methyl group bonded to it versus the 3 carbon having an ethyl group instead.  You do not satisfy (2), so you do not have the symmetry required for a meso compound, and the molecule is still chiral and optically active.