meso-Tartaric acid is drawn as a Fischer projection with $\mathrm{COOH}$ at the top and bottom, and both OH groups on the right (C2 and C3). The Fischer projection corresponds to the eclipsed conformation about C2-C3. The rear carbon is then rotated by $180^{\circ }$ about the C2-C3 bond to give a staggered conformation. In that staggered conformation:

1. Athe OH/OH dihedral angle is $180^{\circ }$, the $\mathrm{COOH}$/$\mathrm{COOH}$ dihedral angle is $180^{\circ }$ and the conformer has a centre of inversion
2. Bthe OH/OH dihedral angle is $180^{\circ }$ but the $\mathrm{COOH}$/$\mathrm{COOH}$ dihedral angle is $60^{\circ }$, so the conformer is chiral
3. Cthe OH/OH dihedral angle stays $0^{\circ }$ because rotation does not change the Fischer arrangement
4. Dthe OH/OH dihedral angle is $60^{\circ }$ and the conformer has a mirror plane