Write a general note on carbohydrates. Give the classification of carbohydrates.

(N/A) Carbohydrates are primarily produced by plants and form a very large number of naturally occurring organic compounds. Some common examples are sugar,glucose,and starch. Most have the general formula $C_{x}(H_{2}O)_{y}$ and were historically considered hydrates of carbon. For example,glucose $(C_{6}H_{12}O_{6})$ fits this formula as $C_{6}(H_{2}O)_{6}$. However,not all compounds fitting this formula are carbohydrates (e.g.,acetic acid,$CH_{3}COOH$),and some carbohydrates do not fit this formula (e.g.,rhamnose,$C_{6}H_{12}O_{5}$).
Chemically,carbohydrates are defined as optically active polyhydroxy aldehydes or ketones,or compounds that produce such units on hydrolysis. They are also called saccharides. Those sweet in taste are called sugars (e.g.,sucrose,lactose).
Classification based on hydrolysis:
$1$. Monosaccharides: Simplest carbohydrates that cannot be hydrolyzed further. They contain $3$ to $7$ carbon atoms. They are called aldose if they contain an aldehyde group and ketose if they contain a ketone group.

$Carbon \ atoms$	$General \ term$	$Aldehyde$	$Ketone$
$3$	Triose	Aldotriose	Ketotriose
$4$	Tetrose	Aldotetrose	Ketotetrose
$5$	Pentose	Aldopentose	Ketopentose
$6$	Hexose	Aldohexose	Ketohexose
$7$	Heptose	Aldoheptose	Ketoheptose

$2$. Oligosaccharides: Carbohydrates that produce $2$ to $10$ monosaccharide units on hydrolysis. Disaccharides are the most common.
$3$. Polysaccharides: Carbohydrates that yield a large number ($100$ to $3000$) of monosaccharide units on hydrolysis (e.g.,starch,cellulose). They are non-sugars.
Carbohydrates are also classified as reducing or non-reducing sugars based on their ability to reduce Fehling's and Tollen's reagents.