Read the passage carefully and answer the questions:
Optically active polyhydroxy aldehydes or ketones or molecules which provide such units on hydrolysis are called carbohydrates. They can be broadly classified as monosaccharides, disaccharides and polysaccharides depending on their behavior towards hydrolysis. They are also classified as reducing or non reducing sugars. Another class of biomolecules is proteins which are polymers of twenty different amino acids linked by peptide bonds. Amino acids can be classified as acidic, basic or neutral depending on the relative number of amino and carboxyl groups in their molecule. The essential amino acids cannot be synthesized by our body and hence must be provided through diet. Nucleic acids are the polymers of nucleotides which in turn consist of a base, pentose sugar and phosphate. There are two types of nucleic acids namely, DNA and RNA which differ in the composition of sugar and a base.
"Maltose" disaccharide is composed of
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Two \(\alpha\)-D-glucose units
On hydrolysis a disaccharide gives back its two monosaccharide units; maltose gives only D-glucose:
\( \displaystyle \ce{C12H22O11 + H2O} \xrightarrow{\ce{H+}} \ce{2C6H12O6}\ (\text{D-glucose}) \)
Why the other options are incorrect
Option (2) \(\alpha\)-D-glucose and \(\beta\)-D-fructose — Incorrect. These are the units of sucrose, joined C1 to C2.
Option (3) \(\beta\)-D-galactose and \(\beta\)-D-glucose — Incorrect. These are the units of lactose (milk sugar), joined C1 of galactose to C4 of glucose.
Option (4) \(\alpha\)-D-glucose and \(\beta\)-D-glucose — Incorrect. Maltose contains only glucose, but both units are of the α-form; the β-link of glucose units is found in cellulose.
NCERT (2026-27 edition):
Maltose
