Given reason for the following :
(i) Glucose does not give 2, 4 D.N.P. test or Schiff's reagent test.
(ii) Amino acids have high melting points and are water soluble.

Explanation

(i) these are the characteristic reactions of aldehydic (-CHO) group. This group is not free in glucose and is involved in the formation of cyclic structure (`delta` - oxide ring structure). Therefore, glucose does not react with both these reagents.
(ii) Amino acids have dipolar structures and have strong dipole-dipole interaction in their molecules. These have therefore, high melting points. These are water soluble as both the amino `(-NH_(2))` and carboxyl (-COOH) groups are involved in hydrogen bonding with the `H_(2)O` molecules.