Category: Class 12 Chemistry Objective Questions

Chemistry Multiple Choice Questions on “Position of the Periodic Table”.

1. All d-block elements are transition elements.
a) True
b) False
View Answer

Answer: b
Clarification: Scandium and Zinc are d-block elements but are not transition elements. The electronic configurations of Sc and Zn are:
Sc: [Ar] 3d¹4s²
Zn: [Ar] 3d¹⁰4s²
In their ionic form, Sc and Zn lose electrons and attain the configuration of Argon. Hence, they have completely filled d orbitals.

2. What is the general electronic configuration of d-block elements?
a) (n-1)d^1-10ns^0-2
b) ns²np^1-6
c) (n–2)f^1–14(n–1)d^0–10ns²
d) ns^1-2
Answer: a
Clarification: D-block elements are so-called since, in them, 3d, 4d, 5d and 6d subshells are incomplete and the last electron enters the (n-1)d orbital, i.e., penultimate (last but one) shell. Their general electronic configuration is (n-1)d^1-10ns^0-2, where n is the outermost shell.

3. How many series’ of transition elements are present in the periodic table?
a) One
b) Two
c) Three
d) Four
Answer: d
Clarification: Unlike s or p block elements which are usually discussed as columns or groups, d-block elements are better discussed by classifying them into horizontal series. In the periodic table, there are four main transition series of elements corresponding to filling of 3d, 4d, 5d and 6d sublevels in the 4^th, 5^th, 6^th and 7^th periods.

4. The study of transition elements is useful.
a) True
b) False
Answer: a
Clarification: The study of transition elements is important because precious metals such as silver, gold and platinum as well as industrially important metals such as iron, copper and titanium are transition elements.

5. Which of the following element is not a transition element?
a) Fe
b) Mn
c) Zn
d) Ag
Answer: c
Clarification: All transition elements are d-block elements, but all d-block elements are not transition elements. Zinc has the electronic configuration [Ar] 3d¹⁰4s², and the configuration of the Zn²⁺ ion is [Ar] 3d¹⁰. Thus, both the element and its only known stable ion have completely filled d-orbitals. Also, the metal does not exhibit any variable valency or multiple oxidation states in compound formation.

6. Which of the following element belongs to the first transition series of the periodic table?
a) V
b) Zr
c) Ta
d) Y
Answer: a
Clarification: The first transition series or 3d series corresponding to the filling of 3d sublevel consists of the following 10 elements of the 4^th period: Sc (Atomic No. = 21), Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn (Atomic No. = 30).

7. Which of the following element belongs to the second transition series of the periodic table?
a) Ni
b) Au
c) La
d) Nb
Answer: d
Clarification: The second transition series or 4d series corresponding to the filling of 4d sublevel consists of the following 10 elements of the 5^th period: Y (Atomic No. = 39), Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag and Cd (Atomic No. = 48).

8. Which of the following element belongs to the third transition series of the periodic table?
a) Sc
b) Re
c) Rh
d) Tc
Answer: b
Clarification: The third transition series or 5d series corresponding to the filling of 5d sublevel consists of the following 10 elements of the 6^th period: La (Atomic No. = 57); Hf (Atomic No. = 72), Ta, W, Re, Os, Ir, Pt, Au and Hg (Atomic No. = 80).

9. What is the first element of the fourth transition series in the periodic table?
a) Scandium
b) Yttrium
c) Actinium
d) Lanthanum
Answer: c
Clarification: The fourth transition series or 6d series corresponding to the filling of 6d sublevel starts with Actinium (Atomic No. = 89) followed by elements with atomic number 104 onwards. These elements lie in the seventh period of the periodic table.

10. What is the nature of the transition elements?
a) Metallic
b) Non-metallic
c) Metalloid
d) Varies from element to element
Answer: a
Clarification: Because they are all metals, the transition elements are often called the transition metals. As a group, they display typical metallic properties and are less reactive than the metals in group 1 and group 2 of the periodic table.

Chemistry Multiple Choice Questions on “Bonding in Metal Carbonyls”.

1. What is the geometry of pentacarbonyliron(0)?
a) Square planar
b) Tetrahedral
c) Trigonal bipyramidal
d) Octahedral
Answer: c
Clarification: The coordination number of pentacarbonyliron(0) is 5 as CO is a unidentate ligand and hence its geometry id trigonal bipyramidal.

2. The following structure of a carbonyl compound is formed by which transition metal.

a) Ni
b) Cr
c) Mn
d) Co
Answer: d
Clarification: There are 8 carbonyl ligands present. This compound is formed by cobalt metal ion an is named octacarbonyldicobalt(0). It also has Co-Co bond bridged by two carbonyl groups.

3. The metal-carbon bond in metal carbonyls possesses only sigma character.
a) True
b) False
Answer: b
Clarification: The M-C bond in metal carbonyls has both sigma and pi bonds and this helps in creating a synergic effect and, hence strengthening the bond.

4. How is the M-C pi bond formed?
a) Donation of electron pair of half-filled metal d orbital to empty bonding pi orbital of CO
b) Donation of electron pair of filled metal d orbital to empty bonding pi orbital of CO
c) Donation of electron pair of filled metal d orbital to empty antibonding pi orbital of CO
d) Donation of electron pair of half-filled metal d orbital to empty antibonding pi orbital of CO
Answer: c
Clarification: The pi bond involves donation of electrons from filled metal d orbitals into empty antibonding pi orbitals of CO. This is also called a back bond.

5. The donation of lone pair of electrons of CO carbon into the vacant orbital of metal atom results in _________ bond.
a) sigma
b) pi
c) back
d) synergic
Answer: a
Clarification: Synergic bonding is the overall effect of the sigma and pi interactions in metal carbonyl bonds. M-C pi bonds are also known as back bonding.

Chemistry Multiple Choice Questions on “Structures of Functional Groups”.

1. How many lone pairs of electrons does O atom have in methanol?
a) 0
b) 1
c) 2
d) 4
Answer: c
Clarification: The oxygen atom in methanol is sp³ hybridised. One of the sp³ orbitals overlaps with 1s orbital of hydrogen (of OH group) and one sp³ orbital overlaps with sp³ orbital of C atom. The remaining two sp³ orbitals contain one lone pair of electrons each.

2. What is the value of C-O-H bond angle in phenol?
a) 108°
b) 108.9°
c) 109°
d) 109.8°
Answer: c
Clarification: The bond angle C-O-H in phenols is 109° which is slightly more than the C-O-H bond angle in methanol (108.9°) and slightly less than the tetrahedral bond angle (109.5°).

3. If A and B are the C-O bond lengths in methanol and phenol respectively, what is the relationship between A and B?
a) A>B
b) Ac) A=B
d) A≥B

Answer: a
Clarification: The C-O bond length in methanol is 142pm, whereas the C-O bond length in phenol is 136pm, which is slightly less than that in methanol.

4. Which of the following is not a correct reason for the C-O bond length in phenol to be less than that in methanol?
a) Partial double bond character of C-O bond
b) Conjugation of lone pair of electrons with the aromatic ring
c) sp² hybridised sate of carbon of C-O bond
d) Repulsion between the electron lone pairs of oxygen
Answer: d
Clarification: The two lone pairs of electrons of oxygen are present in OH groups of both phenol and methanol and has an effect on the C-O-H bond angle and not the C-O bond length.

5. If the dipole moment of methanol is 1.71D, predict the dipole moment of phenol.
a) 1.54D
b) 1.71D
c) 1.89D
d) 1.96D
View Answer

Answer: a
Clarification: Phenol has a smaller dipole moment than methanol because the C-O bond in phenols is polar due to the electron withdrawing effect of the aromatic ring.

6. The C-O-C bond angle in ethers is _______
a) lesser than 109.5°
b) 109.5°
c) greater than 109.5°
d) 180°
View Answer

Answer: c
Clarification: Due to the repulsive interaction of the bulky alkyl/aryl groups in ethers, the bond angle is slightly more than the tetrahedral angle, i.e., 109.5°. For example, the C-O-C bond angle in methoxymethane is 111.7°.

7. In methanol, the O-H bond length is smaller than the C-O bond length.
a) True
b) False
Answer: a
Clarification: Since hydrogen atom is smaller than the carbon atom and has only 1s orbital, the O-H bond (96pm) is much smaller than the C-O bond (142pm).

8. If the C-O bond length in methanol is 142pm, what will be the C-O bond length in the given compound?

a) 96pm
b) 121pm
c) 141pm
d) 202 pm
Answer: c
Clarification: The shown compound in methoxymethane which is an ether. The C-O bond length in ethers is almost the same as that in alcohols.

Chemistry Multiple Choice Questions on “Carboxylic Acids Physical Properties”.

1. Which of the following aliphatic carboxylic acids is a solid at room temperature?
a) Heptanoic acid
b) Octanoic acid
c) Nonanoic acid
d) Decanoic acid
Answer: d
Clarification: The members butanoic acid to nonanoic acid are colourless oily liquids at room temperature. The compounds with ten or more carbon atoms exists as waxy solids at room temperature.

2. Which among the following has the most unpleasant odour?
a) Caproic acid
b) Lauric acid
c) Myristic acid
d) Palmitic acid
Answer: a
Clarification: The first three members of carboxylic acids have pungent smell. The next six members have a faint unpleasant odour. The higher members (lauric acid, myristic acid, palmitic acid) are practically odourless due to their low volatility.

3. Benzoic acid is almost insoluble in which of the following solvents?
a) Cold water
b) Benzene
c) Ether
d) Alcohol
Answer: a
Clarification: The large hydrophobic benzene ring of benzoic acid prevents the carboxyl group from taking part in hydrogen bonding. However, benzoic acid is soluble in non-polar solvents like benzene, ether, alcohol, chloroform, etc.

4. The solubility of carboxylic acids _________ with the increase in size of alkyl groups.
a) increases
b) decreases
c) remains same
d) varies unpredictably
Answer: b
Clarification: This is because of the reduced polarity and hinderance provided by the large alkyl groups to the COOH group from involving in the hydrogen bonding with solvent molecules.

5. As a result of intermolecular hydrogen bonding, carboxylic acids exists as ______
a) acetals
b) aldols
c) hemiacetals
d) dimers
Answer: d
Clarification: The intermolecular hydrogen bonds between carboxylic acids are not broken even in vapour phase. In fact, most carboxylic acids exist as dimer in vapour phase or in aprotic solvents.

6. Which of the following is not a reason for carboxylic acids having higher boiling point than alcohols of comparable molecular masses?
a) Presence of electron withdrawing carbonyl group
b) Higher polarity of OH bond than in alcohols
c) Formation of two hydrogen bonds to form cyclic dimers
d) Presence of more alkyl groups in carboxylic acids
Answer: d
Clarification: The OH bond in carboxylic acids is more strongly polarised due to the presence of adjacent electron withdrawing CO group. This results in stronger hydrogen bonds. Also, the presence of alkyl groups should increase the polarity of OH bond as they are electron releasing in nature. Furthermore, carboxylic acids form two hydrogen bonds between molecules compared to the only one between alcohols.

7. What is the correct order of boiling points of the following?
a) HCOOH > CH₃COOH > C₂H₅COOH
b) C₂H₅COOH > CH₃COOH > HCOOH
c) HCOOH > C₂H₅COOH > CH₃COOH
d) CH₃COOH > HCOOH > C₂H₅COOH
Answer: b
Clarification: The boiling points increase with the increase in molecular mass, because as the size of alkyl group increases, the magnitude of van der Waal forces increases, thus making the bonds difficult to break.

8. If the boiling point of propanol is 370 K, predict the boiling point of acetic acid.
a) 322 K
b) 329 K
c) 370 K
d) 390 K
Answer: d
Clarification: Acetic acid and propanol both have same molecular mass. Acetic acid should have a higher boiling point than propanol because of its stronger hydrogen bonds and the fact that it forms cyclic dimers.

9. Boiling point of aromatic carboxylic acids are higher than that of comparable aliphatic carboxylic acids.
a) True
b) False
Answer: a
Clarification: This is because benzene ring has a planar structure and can pack more closely in the crystal lattice than aliphatic acids, which have a zig-zag structure. The melting of aromatic acids are also usually higher due to the same reason.

Chemistry Multiple Choice Questions on “Preparation Method of Diazonium Salts”.

1. What is the most suitable temperature for the diazotisation reaction to take place?
a) 0°C
b) 10°C
c) 22°C
d) 30°C
Answer: a
Clarification: Benzene diazonium salts are prepared by the reaction of aniline with nitrous acid at very low temperatures (273-278K). If the temperature was to cross 278K, phenol will be formed instead.

2. Identify the diazonium group in the diazonium salt ArN₂⁺Br-.
a) ArN₂⁺
b) N₂⁺Br^–
c) N₂⁺
d) ArN₂Br
Answer: c
Clarification: The Ar represents the aromatic ring and Br^– is the negative ion that forms the salt by combining with the diazonium group, N₂⁺.

3. What is the correct name of the compound C₆H₅N₂⁺HSO₄^–?
a) Benzenediazonium hydrogensulphate
b) Benzenehygrogensulphate diazonium
c) Diazonium benzenehydrogensulphate
d) Hydrogensulphate diazoniumbenzene
Answer: a
Clarification: Diazonium salts are named by suffixing diazonium to the parent hydrocarbon (benzene) from which they are formed, followed by the name of the anion (HSO₄^–).

4. Identify the reagent ‘X’ in the following reaction.

a) HNO₃
b) NaNO₂ and HCl
c) NaCl and HNO₃
d) NaNO₂ and H₂SO₄
Answer: b
Clarification: Aniline actually reacts with HNO₂ (nitrous acid) at 273K to form Benzenediazonium chloride. But this nitrous acid in produced in situ, by a mixture of NaNO₂ and HCl.

5. Why is the reason for the stability of aromatic diazonium salts?
a) Dispersal of negative charge over the benzene ring
b) Dispersal of positive charge over benzene ring
c) Bond between diazonium group and anion
d) High electronegativity of anion compared to the N atom
View Answer

Answer: b
Clarification: The stability of benzenediazonium salt is due to its resonance structures. In three of the resonance structures, the positive charge is dispersed over the benzene ring at ortho and para positions.

6. Aliphatic diazonium salts are highly unstable.
a) True
b) False
View Answer

Answer: a
Clarification: Alkyldiazonium salts are highly unstable as they readily decompose at low temperatures forming a carbocation and nitrogen gas.

7. The preparation of diazonium salts from primary aromatic amines is known as ______
a) acylation
b) alkylation
c) benzonation
d) diazotisation
View Answer

Answer: d
Clarification: This is a method of preparation of diazonium salts. This occurs by the formation of nitrosonium ion followed by diazohydroxide, which on protonation gives diazonium ion. This takes up the acid anion to form diazonium salt.

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Chemistry Multiple Choice Questions on “Classification of Polymers”.

1. Which of the following is a co-polymer?
a) Polythene
b) Bakelite
c) PVC
d) Polyacrylonitrile
Answer: b
Clarification: A polymer formed from on type of monomer is called a homopolymer. Polythene, PVC and PAN are homopolymers. A polymer formed from two or more different monomers is a co-polymer or a mixed polymer.

2. Polymers are not classified on the basis of which of the following?
a) Source
b) Number of monomers
c) Method of preparation
d) Structure
Answer: b
Clarification: Polymers are very large molecules formed by joining together huge number of simple units, or monomers. They are mainly classified on the basis of their source, structure, mode of synthesis and molecular forces.

3. Which of the following types of polymers is not based on the classification by the source?
a) Natural
b) Semi-synthetic
c) Elastomers
d) Synthetic
Answer: c
Clarification: On the basis of source, polymers are classified as natural, semi-synthetic or synthetic. Elastomers are a class of polymers based on the molecular forces.

4. Which of the following is not a natural polymer?
a) Rayon
b) Starch
c) Cellulose
d) RNA
View Answer

Answer: a
Clarification: The polymers obtained from plants and animals are called natural polymers. Rayon is a semi-synthetic polymer which is derived from a natural polymer by chemical modification. Cellulose on acetylation with acetic anhydride in sulphuric acid gives cellulose acetate polymer or rayon.

5. Which of the following polymers has a structure as shown?

a) Low-density polythene
b) High-density polythene
c) Polyvinyl chloride
d) Bakelite
View Answer

Answer: a
Clarification: The shown structure has unconnected linear chains with some intermediate branches. This is a branched chain polymer. They are irregularly packed and have lower density and strength than linear polymers.

6. All macromolecules are polymers.
a) True
b) False

Answer: b
Clarification: Polymers consists of thousands of repeating units, and are macromolecules because of their very large size and high molecular mass (10³ to 10⁷ u). However, a macromolecule may or may not contain repeating monomer units (for example, chlorophyll). Therefore, all polymers are macromolecules, but all macromolecules are not polymers.

7. The synthesis of which of the following polymers involves the repeated loss of small molecules?
a) Polythene
b) Buna-S
c) Buna-N
d) Nylon-6,6

Answer: d
Clarification: Condensation polymers are formed by the repeated condensation reaction between two different bi-functional or tr-functional monomeric units, along with the loss of small molecules like water, alcohol, HCl, etc. Nylon-6,6 is formed by the condensation of hexamethylene diamine and adipic acid, resulting in loss of water molecules.

8. The compound [-CH₂-CH(C₆H₅)^–]_n is a ________
a) homopolymer
b) co-polymer
c) condensation polymer
d) network polymer
View Answer

Answer: a
Clarification: [-CH₂-CH(C₆H₅)^–]_n is a homopolymer with a linear structure. It is obtained from the addition polymerisation of the monomer styrene, C₆H₅CH=CH₂.

9. Which of the following is not an elastomer?
a) Buna-S
b) Buna-N
c) PVC
d) Neoprene
Answer: c
Clarification: Elastomers are polymers that have rubber like elastic properties. The polymer chains are held together by the weakest intermolecular forces, which facilitate the stretching of the polymer. PVC is a plastic and not an elastomer.

10. Which of the following fibres does not have dipole-dipole interactions?
a) Nylon
b) Terylene
c) Dacron
d) Orlon
Answer: a
Clarification: Fibres are polymers which have strong intermolecular forces between the chains, either by hydrogen bonding or dipole-dipole interactions. In case of polyamides (nylon), the forces are hydrogen bonding, whereas in polyesters (terylene, dacron) and polyacrylonitriles (orlon) it is dipole-dipole interactions.

11. What are the intermolecular forces in acrilan?
a) Hydrogen bonds
b) Dipole-dipole interaction between carbonyl groups
c) Dipole-dipole interaction between carbonyl and cyano groups
d) Van der Waals forces
Answer: c
Clarification: Acrilan is a fibre of polyacrylonitrile. It forms strong intermolecular bonds through dipole-dipole interactions between the carbonyl and cyano groups.

12. Which of the following has the weakest intermolecular forces?
a) Buna-N
b) Nylon-6,6
c) Polythene
d) Polystyrene
Answer: a
Clarification: Elastomers (buna-N) have the weakest intermolecular forces whereas fibres (nylon-6,6) have very strong intermolecular forces due to hydrogen bonds and dipole-dipole forces. Thermoplastic polymers (polythene, polystyrene) have intermolecular attractions intermediate to that of elastomers and fibres.

13. The polymer shown is a _______

a) elastomer
b) fibre
c) thermoplastic
d) thermosetting plastic
Answer: c
Clarification: The shown polymer is polyvinyl chloride. It is a dense linear polymer which is capable of repeatedly softening on heating and hardening on cooling.

14. ________ undergoes permanent deformation on heating.
a) Polythene
b) PVC
c) Teflon
d) Bakelite
Answer: d
Clarification: Bakelite is a cross-linked thermosetting polymer, which on heating undergoes extensive cross-linking and undergo permanent change. They cannot be reused.

15. Terylene is a thermoplastic polymer prepared from addition polymerisation.
a) True
b) False
Answer: b
Clarification: Terylene, also known as polyethylene terephthalate, is a thermoplastic polymer of the polyester family. Terylene is made from the condensation polymerisation of terephthalic acid and ethylene glycol.