Answer : (C) Ascorbic acid

Step 1 — Recall the chemical name of vitamin C

Vitamin C is ascorbic acid, with the molecular formula $C_6H_8O_6$.

Step 2 — Note its key properties

It is a water-soluble vitamin, so the body cannot store it — any excess is excreted in the urine and it must therefore be taken regularly in the diet.

Its deficiency causes scurvy, marked by bleeding, spongy gums and slow healing of wounds.

Rich sources are citrus fruits, amla (Indian gooseberry) and green leafy vegetables.

Step 3 — Identify the other acids

Saccharic acid (glucaric acid) — obtained by oxidising glucose with concentrated $HNO_3$; both end groups become $-COOH$.

Gluconic acid — obtained by oxidising glucose with bromine water; only the $-CHO$ group is affected.

Benzoic acid — a simple aromatic acid, $C_6H_5COOH$, with no vitamin role.

Step 4 — Conclude

Only ascorbic acid is a vitamin; the others are ordinary organic acids.