the answer is b) ihexpression is <xp-> - <px> , this is commutator of position operator x and momentum p, which in quantum mechanics is defined as [x,p] = xp-pxfrom canonical commutation we know that [x,p] = ihso xp-px = ih, where h is reduced planck's constant [h(line) = h/(2pi)]so ultimately, <[x,p]>=<xp>-<px>=ih(h with the line)