Category: Class 12 Chemistry Objective Questions

Chemistry Multiple Choice Questions on “Alcohols, Phenols and Ethers Classification”.

1. What is the general formula for an aliphatic alcohol? (R=alkyl group)
a) R-H
b) R-OH
c) R-CHO
d) R-COOH
View Answer

Answer: b
Clarification: Alcohols are compounds having OH group attached to an alkyl group and are hence hydroxy derivatives of hydrocarbons.

2. Which of the following is true regarding polyhydric alcohols?
a) It should have one or more OH groups
b) It should have two or more OH groups
c) It should have three or more OH groups
d) It should have more than four OH groups
Answer: b
Clarification: Alcohols may be classified as mono-, di- tri- or polyhydric depending on whether it has one, two, three or more OH groups in its structure. Di- and trihydric alcohols are also classified as polyhydric.

3. Which of the following types of alcohol contain a bond between sp² hybridised carbon and OH group?
a) Primary allylic alcohols
b) Secondary allylic alcohols
c) Tertiary allylic alcohols
d) Vinylic alcohols
Answer: d
Clarification: Allylic alcohols are those in which OH group is attached to a sp³ hybridised carbon adjacent to a C-C double bond, i.e., an allylic carbon. Whereas, vinylic alcohols contain OH group attached directly to a C-C double bond.

4. Which of the following terms does not describe CH₂=CH-CH₂OH?
a) Primary
b) Monohydric
c) Allylic
d) Vinylic
Answer: d
Clarification: The given compound contains a sp³ hybridised C-OH bond and is allylic. Ince it has only one alkyl group attached to the C bonded to the OH group, it is primary and the presence of only one OH group makes it monohydric.

5. Choose the most suitable classification for the shown compound?

a) Secondary alcohol
b) Allylic alcohol
c) Dihydric alcohol
d) Benzylic alcohol
Answer: b
Clarification: The compound shown is a monohydric, tertiary alcohol in which the OH group is attached to the C next to a C-C double bond, hence make it allylic.

6. Primary alcohols van be benzylic in nature.
a) True
b) False
Answer: a
Clarification: Benzylic alcohols contain a sp³ C-OH bond next to an aromatic ring, which means that the C atom can have zero or two alkyl groups attached to it along with the ring and OH group.

7. Which of the following is not a vinylic alcohol?
a) CH₂=CH-OH
b) HO-CH=CH-CH₃
c) CH₂=CH-CH₂-OH
d) CH₃-CH₂-CH=CH-OH

Answer: c
Clarification: Vinylic alcohols contain an OH group bonded to a sp² hybridised carbon of a double bond. CH₂=CH-CH₂-OH is an allylic alcohol.

8. Which of the following compounds contain an aryl carbon?
a) Ethanol
b) Benzyl alcohol
c) Vinyl alcohol
d) Phenol

Answer: d
Clarification: The sp² hybridised carbon of an aromatic ring to which the hydroxyl group is attached is called an aryl carbon. In phenol, the OH group is attached to an aryl carbon.

9. R-O-R, where R represent an alkyl or aryl group is the general formula of which compound?
a) Ether
b) Ester
c) Aldehyde
d) Ketone
View Answer

Answer: a
Clarification: Ethers are compounds where the hydrogen of a hydrocarbon is replaced by an alkoxy or aryloxy group. It may also be thought of as compounds formed when the hydrogen of the OH group of an alcohol is replaced by an alkyl or aryl group.

10. When the alkyl groups attached to either side of the oxygen atom of an ether id different, it is known as _______ ether.
a) simple
b) symmetrical
c) mixed
d) diethyl
Answer: c
Clarification: If the alkyl or aryl groups on either side of O atom is different, it is known as a mixed or unsymmetrical ether.

11. Identify the simple ether from the following.
a) CH₃OC₂H₅
b) C₂H₅OC₆H₅
c) C₆H₅OCH₃
d) C₆H₅OC₆H₅
Answer: d
Clarification: Since C₆H₅OC₆H₅ has the same aromatic ring on both sides of the oxygen atom, it a simple or symmetrical ether.

12. Which of the following is not an aromatic ether?
a) CH₃-O-C₆H₅
b) CH₃-O-CH₂CH₃
c) C₂H₅-O-C₆H₅
d) C₆H₅-O-C₆H₅
Answer: b
Clarification: Aromatic ethers are those in which at least one of the groups on either side of O atom is an aryl group. In CH₃-O-CH₂CH₃, both the groups are alkyl and is hence an aliphatic ether.

13. Diethyl ether is a mixed ether.
a) True
b) False
Answer: b
Clarification: Diethyl ether consists of ethyl (C₂H₅) groups on either side of O, hence it is a simple symmetrical ether.

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Chemistry Multiple Choice Questions on “Uses of Aldehydes and Ketones”.

1. Which of the following is used in the preservation of biological specimens?
a) Methanal
b) Ethanal
c) Acetone
d) Benzaldehyde
View Answer

Answer: a
Clarification: Methanal is easily soluble in water and is commercially sold as formalin (40% methanal, 8% methanol, 52% water) and is used for preserving biological specimens.

2. Which of the following is not a use of formaldehyde?
a) Preservation of biological specimens
b) Manufacturing of bakelite
c) Silvering of mirrors
d) Preparation of acetic acid.
Answer: d
Clarification: Formaldehyde consists of only a single carbon atom and cannot be used as a starting compound for the preparation of acetic acid. However, it is used in the manufacture of bakelite, glues and polymeric products. It also acts as a reducing agent in the silvering of mirrors.

3. Which of the following carbonyl compounds are known for their pleasant odour?
a) Vanillin
b) Acetophenone
c) Acetone
d) Camphor
Answer: c
Clarification: Acetone belongs to the lower sizes of ketones and is less fragrant than the higher compounds like acetophenone, camphor and vanillin which are used as flavouring agents in different industries.

Chemistry Multiple Choice Questions on “Amines Chemical Reactions – 2”.

1. If p, q and r are the pK_b values of methylamine, N-methylamine and N,N-dimethylamine respectively, what is the correct order of p, q and r?
a) p > q > r
b) r > q > p
c) q > p > r
d) r > p > q
Answer: d
Clarification: This peculiar order of basic strength is due to a combination of inductive, solvation and stearic effects of the alkyl groups in the amines. In methyl substituted amines, the solvation effect superimposes the inductive effect to make CH₃NH₂ more basic than (CH₃)₃N. The 2° compound is the most basic because of its higher inductive effect than primary amine and higher solvation than tertiary amine.

2. What is the correct order of basic strength of the following ethyl substituted amines in aqueous solution? (R=ethyl group)
a) RNH₂ > R₂NH > R₃N
b) R₂NH > R₃N > RNH₂
c) R₃N > R₂NH > RNH₂
d) R₂NH > RNH₂ > R₃N
Answer: b
Clarification: There is a subtle interplay of inductive effect, solvation effect and stearic hinderance of alkyl groups to determine the order of basicity of alkylamines in aqueous solutions. For ethyl substituted amines, it is 2°>3°>1°

3. If the pK_b value of N,N-diethylethanamine is 3.25, predict the pK_b value of ethanamine.
a) 3.00
b) 3.29
c) 4.75
d) 9.38
Answer: b
Clarification: In ethyl substituted amines (aqueous), the inductive effect has a bigger role than the solvation effect (because the size of ethyl is larger than methyl group), and as a result the basic strength of N,N-diethylethanamine will be higher than that of ethanamine. Thus, the pK_b value of the latter will be very slightly higher than the former.

4. Which of the following aromatic amines has lower pK_b value than ammonia?
a) Benzylamine
b) Benzenamine
c) N-Methylbenzenamine
d) N,N-Dimethylbenzenamine
Answer: a
Clarification: In aryl amines, the N atom is directly attached to the benzene ring. This makes the lone pair of N to be in conjugation with the benzene ring, thus making it less available for protonation. Whereas, benzylamine is a primary arylalkyl amine and has higher basic strength than ammonia.

5. Which of the following amines will be most reactive when treated with HCl?
a) N-Methylmethanamine
b) N,N-Dimethylmethanamine
c) N-Ethylethanamine
d) N,N-Diethylethanamine
Answer: c
Clarification: Between methyl substituted and ethyl substituted aqueous amines, the latter will have relatively higher K_b values due to the ethyl group being larger than methyl group. Of the ethyl substituted amines, the secondary amine will be the most basic because of the combined inductive and solvation effect of alkyl group. Thus, being the most basic, it will react faster with HCl.

6. How many more resonating structures does aniline have than anilinium ion?
a) 2
b) 3
c) 4
d) 5
Answer: b
Clarification: Aniline has five resonating structures, out of which three of them have a positive charge on nitrogen. This results in unavailability of electron pair for protonation. When aniline accepts a proton, it forms anilinium ion which has only two resonating structures and is less stable and more basic than aniline.

7. Which of the following groups when present at para position increases the basic strength of aniline?
a) NO₂
b) Br
c) NH₂
d) COOH
Answer: c
Clarification: Electron donating groups at para position release electrons towards the nitrogen atom, stabilizes the anilinium cation and hence increase the basic strength. Since NH₂ is an electron donating group, p-phenylenediamine will be more basic than aniline.

8. Identify X if the shown compound has a higher pK_b value than aniline.

a) OH
b) CH₃
c) NH₂
d) Cl
Answer: d
Clarification: The compound has a higher pK_b value than aniline means that it has a lower acidic strength than aniline. This is possible is X is an electron withdrawing group (Cl) that destabilizes the anilinium cation and reduces the basic strength.

9. 4-Aminobenzoic acid has a lower pKa value compared to aniline.
a) True
b) False
Answer: a
Clarification: Lower pK_a value means more acidic, that is less basic, which means a higher pK_b value than aniline. 4-Aminobenzoic acid can be thought of as aniline with COOH group substituted at para position. Since COOH is electron withdrawing in nature, it reduces the basic strength of aniline.

10. Which of the following is the least basic amine?
a) p-Bromoaniline
b) p-Chloroaniline
c) p-Nitroaniline
d) p-Aminobenzonitrile
View Answer

Answer: c
Clarification: All the compounds can be considered as aniline with an electron withdrawing (deactivating) group substituted at the para position to NH₂. Since nitro group is the most deactivating group compared to halogen and cyanide, p-nitroaniline is the least basic compound.

11. Which of the following will have the highest pK_b value?
a) C₆H₅NH₂
b) p-C₆H₅(CH₃)NH₂
c) p-C₆H₅(OCH₃)NH₂
d) p-C₆H₅(NH₂)NH₂
Answer: a
Clarification: CH₃, OCH₃ and NH₂ are all electron donating groups. When these are substituted at para position in aniline, it stabilizes the respective anilinium ion formed and thus increases the basic strength. Therefore, aniline is the weakest base from the given compounds and will have the highest pK_b value.

12. Identify the correct order of basic strength of the following substituted anilines?
a) p-Methylaniline > m-Methylaniline > p-Nitroaniline > m-Nitroaniline
b) p-Methylaniline > m-Methylaniline > m-Nitroaniline > p-Nitroaniline
c) p-Nitroaniline > m-Nitroaniline > p-Methylaniline > m-Methylaniline
d) p-Nitroaniline > m-Nitroaniline > m-Methylaniline > p-Methylaniline
Answer: b
Clarification: The base weakening effect of electron withdrawing group (NO₂) and the base strengthening effect of electron donating group (CH₃) is more prominent at para position than at meta position.

13. If ‘a’ is the pK_b value of aniline and ‘b’, ‘c’ and ‘d’ are the pK_b values of o-, m- and p- isomers of methylaniline respectively, what is the correct order of the values a, b, c and d?
a) a > b > c > d
b) d > c > a > b
c) d > c > b > a
d) b > a > c > d
Answer: d
Clarification: Every ortho substituted aniline (electron withdrawing or electron releasing group) is less basic than aniline and consequently its meta and para isomers. This is because of the ortho effect, which is due to the combination of stearic and electronic factors.

14. If the pK_b value of p-nitroaniline is 13, predict the pK_b value of its ortho isomer?
a) 9.38
b) 11.54
c) 13
d) 14.22
View Answer

Answer: d
Clarification: NO₂ is an electron withdrawing group and has a weakening effect on the basicity of anilines. Its presence at para position will be more influencing than at meta, but less weakening than at ortho position. This anomaly is due to a complex ortho effect (stearic and electronic reasons). Hence o-nitroaniline is a weaker base and has a higher pK_b value than p-nitroaniline.

15. Phenylmethanamine is more basic than benzenamine.
a) True
b) False
Answer: a
Clarification: In arylalkyl amines, the lone pair od electrons on N is not conjugated with the benzene ring and is not delocalized. Hence, the lone pair of electrons on n atom inn arylalkyl amines is more readily available for protonation than that on the N atom of benzenamine.

Chemistry Multiple Choice Questions on “Biomolecules – Vitamins”.

1. Which of the following compounds is usually not produced by the human body?
a) Hormones
b) Nucleic acids
c) Vitamins
d) Enzymes
Answer: c
Clarification: Organic chemical substances which are consumed in small quantities through proper diet are called vitamins. These are essential for the proper maintenance and of health and growth of an individual. These are not synthesized by the human body.

2. Which of the following statement is incorrect?
a) Vitamin deficiency causes diseases
b) Excess vitamin intake is harmful
c) Vitamins contain amino groups
d) Vitamins can be produced by plants
View Answer

Answer: c
Clarification: Plants can synthesize almost all vitamins, and are considered essential food factors. Both deficiency and excess of vitamins affect the health of an individual negatively. Vitamins were earlier identified as compounds containing amino groups, but was later discovered that most of them did not contain amino groups.

3. Which of the following vitamins are soluble in water?
a) A
b) C
c) D
d) E
Answer: b
Clarification: B groups vitamins and vitamin C ae soluble in water and are grouped together. These must be supplied regularly as they are readily excreted and cannot be stored in the body.

4. The condition of excess intake of vitamins is called ________
a) denaturation
b) renaturation
c) avitaminoses
d) hypervitaminoses
Answer: d
Clarification: When there is a high dose of vitamin intake, there is an appearance of toxic symptoms, which leads to a condition called hypervitaminoses. On the other hand, the condition of vitamin deficiency is called avitaminoses.

5. Which of the following vitamins are stored in human tissues?
a) B₁
b) B₂
c) B₆
d) K
Answer: d
Clarification: Fat soluble vitamins are soluble in fat and oil but insoluble in water. They are stored in liver and adipose (fat storing) tissues. The B group vitamins are water soluble.

6. Which of the following water-soluble vitamins are stored in the body?
a) B₂
b) B₄
c) B₁₂
d) C
Answer: c
Clarification: All B group vitamins and vitamin C are water soluble. However, vitamin B₁₂ is not excreted in urine and is instead stored in the body. It is involved in the metabolism of every cell in the body.

7. Vitamin B₂ is also known as _______
a) thiamine
b) riboflavin
c) cobalamin
d) pyridoxine
Answer: b
Clarification: Vitamin B₂ is a water-soluble vitamin with the chemical name riboflavin. Its deficiency causes cheilosis, digestive disorders and burning sensation of the skin.

8. Retinol is vitamin ___
a) A
b) C
c) D
d) K
Answer: a
Clarification: Retinol, also known as vitamin A, is a vitamin found in food. It is a fat-soluble vitamin also called bright eye vitamin. It helps in the prevention of conditions like xerophthalmia and night blindness.

9. Cyanocobalamin is used for the treatment of deficiency of which vitamin?
a) B₂
b) B₁₂
c) E
d) K
Answer: b
Clarification: Cyanocobalamin is the manufactured form of vitamin B₁₂ which is used to treat B₁₂ deficiency, which causes pernicious anaemia. It is obtained from products like fish, meat, eggs, cheese and curd.

10. Deficiency of ascorbic acid in diet causes _______
a) scurvy
b) beri beri
c) rickets
d) cheilosis
Answer: a
Clarification: Ascorbic acid is another name for vitamin C which is highly water-soluble and an important dietary supplement. It is present in citrus fruits and leafy vegetables. Scurvy is a disease caused by the deficiency of vitamin C.

11. The class of compounds showing vitamin E activity are called _______
a) phytomenadiones
b) tocopherols
c) ergocalciferols
d) pyridoxines
Answer: b
Clarification: Vitamin E is also known as tocopherol. Other compounds that behave like vitamin E also belong to this group. Deficiency of this causes muscular weakness and fragility of red blood cells. Its main source is vegetable oils.

12. Which vitamin can be obtained from sunlight?
a) A
b) H
c) D
d) E
Answer: c
Clarification: The skin is capable of producing large amounts of vitamin D when the skin is exposed to sunlight. The part of sunlight that is important is ultraviolet B rays. The deficiency of vitamin D causes rickets and osteomalacia.

13. Deficiency of vitamin K increases the blood clotting time.
a) True
b) False
Answer: a
Clarification: Vitamin K (phylloquinone) is fat-soluble and also known as coagulation vitamin. It helps in clotting of blood and prevents haemorrhage.

14. Deficiency of riboflavin causes beri beri.
a) True
b) False
Answer: b
Clarification: Riboflavin is vitamin B₂, the deficiency of which causes cheilosis and digestive disorders. Beri beri is caused by the deficiency of thiamine, or vitamin B₁.

Chemistry Quiz for Schools on “Solid State – Number of Atoms in a Unit Cell”.

1. In primitive unit cubic cell, only _______ of an atom (or ion or molecule) belongs to a particular unit cell.
a) (frac{1}{4})th
b) (frac{1}{3})rd
c) (frac{1}{8})th
d) (frac{1}{2})nd
Answer: c
Clarification: In primitive unit cubic cell, each atom at the corner is shared between 8 adjacent unit cells. Thus, only (frac{1}{8})th of an atom (or ion or molecule) belongs to a particular unit cell.

2. The total number of atoms in one unit cell of primitive unit cubic cell is ______ atom(s).
a) 1
b) 8
c) 4
d) 2
Answer: a
Clarification: In primitive cubic unit cell, atoms are present only at the corner of the cell. Thus, in actual, only (frac{1}{8})th of an atom (or ion or molecule) belongs to a particular unit cell. Hence, the total number of atoms in primitive cubic unit cell = 8 × (frac{1}{8}) = 1 atom.

3. The total number of atoms in one unit cell of body-centered unit cubic cell is ______ atoms.
a) 4
b) 3
c) 8
d) 2
Answer: d
Clarification: In body-centered cubic unit cell, one atom is present at each of the corners and one atom at its body center.
• 8 corners × (frac{1}{8})th of an atom = 1
• 1 body-centered atom
Thus, the total number of atoms in body-centered cubic unit cell: 1+1=2 atoms.

4. The total number of atoms in one unit cell of face-centered unit cubic cell is ______ atoms.
a) 2
b) 6
c) 4
d) 8
Answer: c
Clarification: In face-centered cubic unit cell, atoms are present at each of the corners and at the centre of the face of the cube.
• 8 corners × (frac{1}{8})th of an atom = 1
• 6 faces × (frac{1}{2}) of an atom = 3
Thus, the total number of atoms in face-centered cubic unit cell: 1+3=4 atoms.

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