How do you explain the presence of an aldehydic group in a glucose molecule?

(N/A) The presence of an aldehydic group in glucose can be explained by its reaction with mild oxidizing agents like bromine water $(Br_2/H_2O)$.
Glucose on oxidation with bromine water gets oxidized to gluconic acid,which is a six-carbon carboxylic acid.
This reaction confirms the presence of a carbonyl group in the form of an aldehyde in the glucose molecule.
The reaction is as follows:
$CHO-(CHOH)_4-CH_2OH \xrightarrow{Br_2/H_2O} COOH-(CHOH)_4-CH_2OH$ (Gluconic acid)