Four carbohydrates: glucose,lactose,sucrose,a | vedclass

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(B) Let us analyze the observations for each carbohydrate:$1$. $I_2$ solution test: Starch gives a blue-violet colour with $I_2$ solution. Since the o

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Lactose

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(B) Let us analyze the observations for each carbohydrate:$1$. $I_2$ solution test: Starch gives a blue-violet colour with $I_2$ solution. Since the observation is 'no violet colour',it is not starch.$2$. Fehling solution test: Glucose and lactose are reducing sugars and give a reddish-brown precipitate with Fehling solution. Sucrose is a non-reducing sugar and does not react with Fehling solution.$3$. Barfoed's test (Copper$(II)$ acetate): This test distinguishes between monosaccharides and disaccharides. Monosaccharides (like glucose) reduce copper$(II)$ acetate to $Cu_2O$ (red precipitate) within $5 \ min$. Disaccharides (like lactose) react very slowly or not at all within $5 \ min$.$4$. Observation $(c)$ indicates it is a reducing sugar (glucose or lactose). Observation $(d)$ indicates it is a disaccharide (lactose) because it does not reduce copper$(II)$ acetate quickly.Therefore,the carbohydrate is lactose.

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