An optically inactive aldaric acid results from oxidation of a monosaccharide that has a plane of symmetry. This occurs when the molecule is meso, meaning it has identical chiral centers with opposite configurations that cancel out optical activity.

For an aldose, oxidation with HNO₃ converts both the aldehyde and primary alcohol to carboxylic acids, forming the aldaric acid. If the original aldose is symmetric (like meso-tartaric acid), the resulting diacid will be optically inactive.

The correct structure is the one that is meso. This is the aldose where the top and bottom halves are mirror images. The second image (from the provided options) depicts D-threose, which upon oxidation gives meso-tartaric acid, an optically inactive aldaric acid.

Final Answer: The second option