Multiple choice

Given below are the Rf values of some amino acids in two different solvents. The chromatography was carried out using whatman paper and the mode was ascending.

   
Amino acid Rf value N – butanol – acetic acid – water
(4 : 1 : 5) N – butanol– pyridine water
(1 : 1 : 1)
Aspartic acid 23 20
Alanine 30 37
Glycine 23 29
Histidine 1 24
Leucine 70 60
Lysine 12 13
Tyrosine 45 63

Which of the following pairs of amino acids will not be completely resolved by N – butanol : acetic acid : water (4 : 1 : 5)?

  1. Aspartic acid and glycine

  2. Histidine and gilycine

  3. Leucine and tyrorine

  4. Alanine and glycine
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A Correct answer
Explanation

In paper chromatography, compounds with identical Rf values in a given solvent system cannot be separated. Aspartic acid and glycine both have Rf=23 in the N-butanol-acetic acid-water (4:1:5) system, meaning they will migrate the same distance and remain unresolved.

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