Q.Give two evidences for presence of formyl group in glucose.

Step 1. Section 14.2.4 (point 3) lists the chemical evidence used to establish that glucose contains a carbonyl group, and specifically that it reacts as a genuine aldehyde -- two of these reactions are cited directly as evidence for the formyl (-CHO) group.

Step 2 (evidence 1). Glucose reacts with hydroxylamine (NH2OH), with loss of water, to form glucose oxime (CH=N-OH-(CHOH)4-CH2OH) -- oxime formation is a classic, diagnostic reaction of an aldehyde (or ketone) carbonyl group.

Step 3 (evidence 2). Glucose also reacts with hydrogen cyanide (HCN) by nucleophilic addition to form glucose cyanohydrin (CH(OH)(CN)-(CHOH)4-CH2OH) -- cyanohydrin formation is likewise a classic, diagnostic addition reaction of an aldehyde (or ketone) carbonyl group. …

Recall the two classic carbonyl-addition reactions cited in section 14.2.4 as chemical evidence for glucose's formyl group: oxime …

• Citing glucose's reducing behaviour (positive Tollens'/Fehling's test) alone without naming a specific carbonyl-addition reaction as one of the 'two evidences' asked for. …