The correct choice is (a) angles placed on same side of gusset plate produce eccentricity about one plane only
To elaborate: Two angle sections can either be placed back-to-back on the same side of gusset plate, or back-to-back on the opposite side of gusset plate. When angles are connected on the same side of gusset plate, the eccentricity is about one plane only, which can be almost eliminated when the same angles are connected on opposite side of gusset plate.