The correct option is D an aldehydic group
Tollens' reagent is a chemical reagent used to determine the presence of an aldehyde, aromatic aldehyde and alpha-hydroxy ketone functional groups. The reagent consists of a solution of silver nitrate and ammonia. The aldehyde group in glucose reacts with Tollens reagent to form gluconic acid and release silver, which forms a coat on the inner surface of the reaction vessel, forming the characteristic 'silver mirror'.
2 [Ag(NH3)2]+ + RCHO + H2O → 2 Ag(s) + 4 NH3 + RCO2H + 2 H+
(Tollens reagent) (silver mirror)