Category: Class 12 Chemistry Objective Questions

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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Chemistry Multiple Choice Questions on “Surface Chemistry – Colloids Classification”.

1. Colloids are classified into lyophobic and lyophilic colloids.
a) True
b) False
Answer: a
Clarification: Based on the interaction between the dispersed and dispersion medium, colloids are classified into two types, lyophilic and lyophobic colloids. Lyophilic colloids are those in which the dispersed phase has high affinity for dispersion medium and lyophobic colloids are those in which the dispersed phase has no affinity or least affinity for the dispersion medium.

2. Which of the following is not an example of lyophilic colloids?
a) Starch solution
b) Gelatin
c) Gum
d) Silver solution
Answer: d
Clarification: Starch solution, gelatin and gum are colloids in which the dispersed phase has very high affinity for the dispersion medium and therefore they are categorized as lyophilic colloids. Silver solution on the other hand is an example of lyophobic colloids.

3. Which of the following is not an example of lyophobic colloids?
a) Gold solution
b) Sulphur solution
c) NaCl solution
d) Blood
Answer: c
Clarification: Gold solution, Sulphur solution and blood are colloids in which the dispersed phase has very low affinity for the dispersion medium and once the dispersed phase and dispersion medium are separated we cannot get the solution directly by remixing the two phases. Therefore they are categorized under lyophobic colloids.

4. Colloids are classified into multi-molecular, macro-molecular and associated colloids.
a) True
b) False
Answer: a
Clarification: Based on the nature of dispersed phase, colloids are classified into multi-molecular, macro-molecular and associated colloids. In multi-molecular colloids a large number of atoms aggregate to form a particle of colloidal size, in macro-molecular colloids molecules dissolve in suitable solvents and give rise to particles of colloidal size. Colloids which behave as a normal strong electrolyte at low concentration but exhibits colloidal properties at higher concentration are known as associated colloids.

5. Which of the following is a characteristic of a multi-molecular colloid?
a) Large number of molecules combine to form a particle of colloidal size
b) A large number of atoms aggregate to form a particle of colloidal size
c) Starch solution is an example of multi-molecular colloid
d) Multi-molecular colloids are normally of the lyophilic type
Answer: b
Clarification: In this type of colloidal solution, a large number of atoms or small molecules aggregate to form a particle of colloidal size, these are normally of lyophobic type. Starch solution is an example of lyophilic colloids and hence is not an example for multi-molecular colloids.

6. Which of the following is false regarding macro-molecular colloids?
a) Protein solution is an example for macro-molecular colloids
b) Man-made macro-molecules like polythene can form such colloids
c) Silver solution can form macro-molecular colloids
d) These are normally of lyophilic type
Answer: c
Clarification: Macro-molecules dissolve in a suitable solvents, gives rise to particles of colloidal size. These are normally of lyophilic type and silver solution is an example for lyophobic and multi-molecular colloids.

7. Which of the following is not an example of associated colloids?
a) Sodium stearate
b) Potassium stearate
c) Gum
d) Detergents
Answer: c
Clarification: Some substances at low concentration behave as true solutions. As the concentration of the solution increases, it turns to be a colloidal solution. These type of colloids are knows as associated solution. Soaps like sodium stearate potassium stearate and detergents are examples of associated colloids whereas gum is an example for lyophilic colloids.

8. Which of the following colloids cannot be formed by direct mixing?
a) Lyophilic colloids
b) Lyophobic colloids
c) Macro-molecular colloids
d) Associated colloids
Answer: b
Clarification: Lyophobic colloids such as metal solutions like gold and silver solution, sulphur solution and blood cannot be prepared directly by mixing. These are prepared by special methods and are irreversible in nature. Once the dispersed phase and medium are separated it is not possible to get the solution by remixing the two phases.

9. Which of the following colloids is most stable?
a) Starch solution
b) Blood
c) Sulphur solution
d) Silver solution
Answer: a
Clarification: Starch solution is most stable among the following because it is a lyophilic colloid and the solutions are highly stable due to the high interaction between the dispersed phase and the dispersion medium.

10. In which of the following, the dispersed phase and medium can be separated by evaporation?
a) Ferric hydroxide solution
b) Sulphur solution
c) Metal in water
d) Starch solution
Answer: d
Clarification: In starch solution, if the dispersed phase and the dispersion medium are separated by evaporation, the colloidal solution can be regained by remixing the dispersed phase and dispersion medium. Hence these are called reversible solutions are highly stable because of the high interaction between the dispersed phase and medium.

Chemistry Multiple Choice Questions on “P-Block Elements – Phosphorus – Allotropic Forms”.

1. Which allotrope of phosphorus is the most stable?
a) White phosphorus
b) Red phosphorus
c) Black phosphorus
d) Phosphine
Answer: c
Clarification: Black phosphorus is thermodynamically, the most stable allotrope of phosphorus and does not burn in air even up to 673 K. It has a sharp melting point of 860 K. Like graphite, it is fairly a good conductor of electricity.

2. Which allotrope of phosphorus is the most reactive?
a) White phosphorus
b) Metal phosphorus
c) Red phosphorus
d) Beta-black phosphorus
Answer: a
Clarification: The three allotropic forms of phosphorus differ widely in their chemical reactivity in which white phosphorus is the most reactive while black and red phosphorus are less reactive. White phosphorus is made up of discrete P₄ tetrahedra which are subjected to very high angular strain as the angles is 60 degrees. This high angular strain makes white phosphorus unstable and highly reactive.

3. Red phosphorus is kept under water to protect it from air.
a) True
b) False
Answer: b
Clarification: White phosphorus is a highly reactive clement and must be stored underwater for safekeeping to prevent it from catching fire spontaneously in the air. In water, white phosphorus reacts with oxygen within hours or days. In water with low oxygen, white phosphorus may degrade to a highly toxic compound called phosphine, which eventually evaporates to the air and is changed to less harmful chemicals.

4. From which type of phosphorus is alpha -black phosphorus formed?
a) Phosphide
b) White phosphorus
c) Black phosphorus
d) Red phosphorus
Answer: d
Clarification: Alpha-black phosphorus is the most stable allotrope of black phosphorus. Alpha-black phosphorus is produced from red phosphorus. When red phosphorus is heated in a sealed tube at 803 K, it forms alpha-black phosphorus.

5. Beta-black phosphorus is prepared by heating white phosphorus.
a) True
b) False
Answer: a
Clarification: Yes, Beta-black phosphorus is prepared by heating white phosphorus at 473 K under high pressure(4000-12000 atm) in an inert atmosphere. It has layered structure in which each phosphorus atom is covalently bonded to three neighbouring phosphorus atoms.

6. Like white phosphorus, which phosphorus also exists as P₄?
a) Black phosphorus
b) Red phosphorus
c) Phosphine
d) Beta-black phosphorus
Answer: b
Clarification: Like white phosphorus, red phosphorus also exists as P₄ tetrahedra but these are joined together through covalent bonds to give a polymeric structure. Because of polymeric structure, its melting point (883 K) is much higher than that of white phosphorus(317 K).

7. Which allotrope of phosphorus does not catch fire easily?
a) White phosphorus
b) Alpha- black phosphorus
c) Beta- black phosphorus
d) Red phosphorus
Answer: d
Clarification: Red phosphorus is a relatively stable allotrope of phosphorus at room temperature. Its ignition temperature(543 K) is much higher than that of white phosphorus(303 K). As a result, it does catch fire easily.

8. White phosphorus can be reconverted to red phosphorus.
a) True
b) False
Answer: a
Clarification: Yes, red phosphorus sublimes on heating giving vapours which are the same as by white phosphorus. When these vapours are condensed, white phosphorus is obtained. This gives us simple method of reconverting red phosphorus into white phosphorus.

9. Which allotrope of phosphorus is also called yellow phosphorus?
a) Black phosphorus
b) Red phosphorus
c) Beta- black phosphorus
d) White phosphorus
Answer: d
Clarification: White phosphorus on exposure to light, it turns yellow. It glows greenish in the dark (when exposed to oxygen) and is highly flammable and pyrophoric (self-igniting) upon contact with air. Therefore it is called yellow phosphorus.

10. What is the allotrope of phosphorus in which P-atom completes its octet?
a) Alpha-black phosphorus
b) Beta-black phosphorus
c) White phosphorus
d) Red phosphorus
Answer: c
Clarification: White phosphorus exists as P₄ units. The four sp³ hybridized phosphorus atoms lie at the corners of a regular tetrahedron with an angle of 60 degree. Each phosphorus atom is linked to three other P-atoms by covalent bonds so that each p-atom completes it octet.