This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Biomolecules Carbohydrates – 1”.
1. Which of the following carbohydrates does not satisfy the formula Cx(H2O)y?
Explanation: Initially, most of the carbohydrates had the general formula Cx(H2O)y. Later on it was found out that few of the compounds either fit into this formula but were not carbohydrates or they did not conform to this formula but were hydrates of carbon.
2. Which of the following carbohydrates does not have the formula C12H22O11?
Explanation: Galactose is a monosaccharide with the formula C6H12O6. Sucrose, allolactose and maltose are disaccharides with the same chemical formula C12H22O11.
3. The compound with the formula C2(H2O)2 is a ______
b) carboxylic acid
Explanation: The compound is acetic acid (CH3COOH). Even though it has the general formula Cx(H2O)y of carbohydrates, it is not one. This is one the flaws of the general formula definition of carbohydrates.
4. Identify the correct formula for the carbohydrate rhamnose?
Explanation: Rhamnose is an example of a carbohydrate that does not satisfy the general formula Cx(H2O)y. Its formula is C6H12O5.
5. Which of the following class of compounds is not a part of the large group of carbohydrates?
a) Polyamino aldehydes
b) Polyhalo aldehydes
c) Polyhydroxy ketones
d) Polyhydroxy carboxylic acids
Explanation: Polyamino aldehydes and polyhalo aldehydes do not contain an OH group. Polyhydroxy carboxylic acids do not contain a CHO or a keto group. These also do not produce OH substituted compounds on hydrolysis.
6. Which of the following carbohydrates is not a sugar?
Explanation: Glucose, fructose and lactose are examples of compounds that are sweet in taste and are called sugars. Cellulose is a non-sugar that is tasteless, water insoluble and amorphous.
7. Which of the following is not a polysaccharide?
Explanation: Polysaccharides are those carbohydrates which yield a very large number of monosaccharide units (>10) on hydrolysis. Stachyose (C24H42O21) is a tetrasaccharide that gives four monosaccharide units on hydrolysis.
8. Identify the monosaccharide from the following.
Explanation: Monosaccharides are the simplest carbohydrates which cannot be hydrolysed into simpler units. Deoxyribose (C5H10O4) is a monosaccharide.
9. Raffinose is an example of a ________
Explanation: Raffinose (C18H32O16) is an oligosaccharide which on hydrolysis gives three different monosaccharides, galactose, glucose and fructose. Hence, it is a trisaccharide.
10. Which of the following disaccharides gives two same monosaccharide units on hydrolysis?
Explanation: When any carbohydrate undergoes hydrolysis and produces two separate units of monosaccharides, it is a disaccharide. The used units that are produced may be same. Maltose on hydrolysis gives two units of glucose itself.
11. Sucrose consists of which of the following monosaccharide units?
a) Fructose, galactose
b) Fructose, glucose
c) Galactose, glucose
d) Glucose, glucose
Explanation: Sucrose is a disaccharide, also known as common sugar, composed of two different monosaccharide units, glucose and fructose, which are obtained on hydrolysis.
12. Which of the following disaccharides does not consist of two glucose units?
Explanation: Lactulose is a disaccharide which is composed of two different monosaccharide units namely, galactose and fructose. Whereas trehalose, cellobiose and isomaltose are disaccharides consisting of two glucose units.
13. All monosaccharides are reducing sugars.
Explanation: All monosaccharides whether aldose or ketose, are reducing sugars. This is because they have an aldehyde group or can tautomerize in solution to form an aldehyde group, which reduces Fehling’s solution and Tollen’s reagent.
14. Which of the following is a non-reducing sugar?
Explanation: Sucrose is a non-reducing disaccharide which cannot convert to an open chain with a free aldehyde group and hence cannot reduce Fehling’s solution and Tollen’s reagent.
15. Glucose is an aldohexose.
Explanation: Glucose is an aldehydic carbohydrate (with CHO) group at end of chain) with six carbon atoms (hexose). Its formula is C6H12O6.
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