question_answer

Directions : (21 - 25)

Case V : Read the passage given below and answer the following questions from 21 to 25.

Carbohydrates are polyhydroxy aldehydes and ketones and those compounds which on hydrolysis give such compounds are also carbohydrates. The carbohydrates which are not hydrolysed are called monosaccharides. Monosaccharides with aldehydic group are called aldose and those which free ketonic groups are called ketose. Carbohydrates are optically active. Number of optical isomers \[=\text{ }{{2}^{n}}\]

Where n = number of asymmetric carbons.

Carbohydrates are mainly synthesised by plants during photosynthesis. The monosaccharides give the characteristic reactions of alcohols and carbonyl group (aldehydes and ketones). It has been found that these monosaccharides exist in the form of cyclic structures. In cyclization, the —OH groups (generally \[{{C}_{5}}\] or \[{{C}_{4}}\] in aldohexoses and \[{{C}_{5}}\] or \[{{C}_{6}}\] in ketohexoses) combine with the aldehyde or keto group. As a result, cycli structures of five or six membered rings containing one oxygen atom are formed, e.g., glucose forms a ring structure. Glucose contains one aldehyde group, one \[1{}^\circ \] alcoholic group and four \[2{}^\circ \] alcoholic groups in its open chain structure.

First member of ketos sugar is

A) ketotriose

B) ketotetrose

C) ketopentose

D) ketohexose.