The structure of the gluconic acid obtained from oxidation of glucose is

The correct answer is Option (1) → 

Core Concept

Gluconic acid is formed when only the aldehyde group (–CHO) of glucose is oxidized to –COOH, while the primary alcohol group remains unchanged.

Reaction

Glucose
CHO–(CHOH)₄–CH₂OH → (Mild Oxidation : Br₂ water) → COOH–(CHOH)₄–CH₂OH

Explanation of Each Option

Option 1 represents oxidation of only the aldehyde group into a carboxylic acid, while the terminal CH₂OH group remains unchanged. This is exactly the definition of gluconic acid formation.

Option 2 shows oxidation of both ends, meaning the alcohol group has also been converted into a carboxylic acid. This corresponds to glucaric acid, not gluconic acid.

Option 3 retains the aldehyde group and oxidizes the alcohol group instead, which does not occur in mild oxidation of glucose.

Option 4 shows both ends oxidized into COOH groups. This is again glucaric acid formed by strong oxidation, not gluconic acid.