Question

which of the following statements about reagents is false?\
sudan iii tests for lipids\
dische diphenylamine tests for dna\
biuret reagent tests for proteins (polypeptides)\
lugols iodine reagent tests for starch\
benedicts reagent tests for starch\
ninhydrin reagent tests for amino acids\
question 30\
which of the following best explains the specificity and result of the dische diphenylamine test?\
it precipitates proteins from a nucleic acid solution, indicating the presence of dna.\
it forms a blue - colored complex with the deoxyribose sugar in dna, allowing differentiation from rna.\
it reacts with the ribose sugar in rna to produce a red color, indicating the presence of rna.\
it stains phosphate groups present in nucleic acids, giving a yellow - brown coloration in dna.\
it binds directly to nitrogenous bases in both dna and rna, producing a violet color.

Explanation:

• Sudan III: Sudan III is a lipid - soluble dye that stains lipids. When lipids are present, Sudan III will dissolve in them, showing a color change (usually orange - red), so the statement "Sudan III tests for Lipids" is correct.
• Dische Diphenylamine: In the Dische Diphenylamine test, the diphenylamine reacts with the deoxyribose sugar in DNA. In an acidic environment, the deoxyribose is hydrolyzed and then reacts with diphenylamine to form a blue - colored complex. RNA does not give this reaction because it has ribose sugar instead of deoxyribose, so the statement "Dische Diphenylamine tests for DNA" is correct.
• Biuret Reagent: The Biuret reagent (contains copper sulfate and sodium hydroxide) reacts with the peptide bonds (-CO - NH -) in proteins (polypeptides). The copper ions in the reagent form a violet - colored complex with the peptide bonds, so the statement "Biuret Reagent tests for Proteins (Polypeptides)" is correct.
• Lugol's Iodine reagent: Lugol's iodine (a solution of iodine in potassium iodide) reacts with starch. The iodine molecules fit into the helical structure of amylose (a component of starch) to form a blue - black complex, so the statement "Lugol's Iodine reagent tests for Starch" is correct.
• Benedict's Reagent: Benedict's reagent is used to test for reducing sugars (such as glucose, fructose, galactose). In the presence of reducing sugars, when heated, the copper (II) ions in Benedict's reagent (copper sulfate) are reduced to copper (I) oxide, which forms a brick - red precipitate. It does not react with starch. Starch is a non - reducing polysaccharide, so the statement "Benedict's Reagent tests for Starch" is false.
• Ninhydrin Reagent: Ninhydrin reacts with amino acids. The amino acids are oxidized and decarboxylated, and the ninhydrin reacts with the resulting ammonia and a reduced form of ninhydrin to form a purple - colored complex (Ruhemann's purple), so the statement "Ninhydrin Reagent tests for Amino Acids" is correct.

For the second question:

• Option 1: Precipitating proteins from a nucleic acid solution is not the function of Dische Diphenylamine. There are other methods (such as using alcohol precipitation for nucleic acids and salting - out for proteins in some cases) to separate proteins from nucleic acids.
• Option 2: The Dische Diphenylamine test specifically reacts with the deoxyribose sugar in DNA. In an acidic medium, the deoxyribose is hydrolyzed to form a compound that reacts with diphenylamine to form a blue - colored complex. RNA has ribose sugar, and this reaction does not occur with ribose in the same way, allowing differentiation from RNA.
• Option 3: Dische Diphenylamine is for DNA (reacting with deoxyribose), not for RNA (ribose). The reaction described in this option is incorrect for the Dische Diphenylamine test.
• Option 4: Staining phosphate groups is not the mechanism of the Dische Diphenylamine test. There are other stains (such as methylene blue which can stain phosphate groups in some contexts) but not Dische Diphenylamine.
• Option 5: Binding to nitrogenous bases in both DNA and RNA is not the mechanism of the Dische Diphenylamine test. The test is specific to the deoxyribose sugar in DNA.

Answer:

• For the first question: The false statement is "Benedict's Reagent tests for Starch".
• For the second question: The correct option is "It forms a blue - colored complex with the deoxyribose sugar in DNA, allowing differentiation from RNA".