250+ TOP MCQs on Laws of Chemical Combination and Answers

Chemistry Multiple Choice Questions on “Laws of Chemical Combination”.

1. How many basic laws are required to govern the combination of elements to form compounds?
a) 6
b) 5
c) 4
d) 1

Answer: b
Clarification: Five basic laws are required to govern the combination of elements to form compounds. They are Law of Conservation of Mass, Law of Definite Proportions, Law of Multiple Proportions, Gay Lussac’s Law of Gaseous Volumes, and Avogadro’s Law.

2. Who proposed Law of Conservation of Mass?
a) Antoine Lavoisier
b) Joseph Proust
c) Lorenzo Romano
d) Joseph Louis

Answer: a
Clarification: Antoine Lavoisier conducted many experiments regarding combustion and noticed various physical and chemical changes and there is no change in overall mass. Hence he came to a conclusion that mass can neither be created nor destroyed i.e. Law of Conservation of Mass.

3. What did Joseph Proust state regarding Law of Definite Proportions?
a) A given mixture always contains absolutely the same proportion of elements by weight
b) A given compound always contains absolutely the same proportion of moles by weight
c) A given compound always contains absolutely the same proportion of elements by volume
d) A given compound always contains absolutely the same proportion of elements by weight

Answer: d
Clarification: When Joseph Proust worked about the composition of elements present in a compound experimentally, he found out that it was the same for all the samples he took. Joseph Louis concluded that from any source, a particular compound always contains the same elements in the same proportion by mass/weight.

4. What did Dalton propose?
a) Law of Multiple Proportions
b) Avogadro’s Law
c) Law of Definite Composition
d) Law of Conservation of Mass

Answer: a
Clarification: Two or more elements those are given, may combine to form more than one compound, the masses of one element that will combine with the given mass of the other elements, would be in the ratio of whole numbers is the law of Multiple Proportions.

5. Who proposed the Law of Definite Composition?
a) Joseph Proust
b) Lorenzo Romano
c) Joseph Louis
d) Antoine Lavoisier

Answer: a
Clarification: Joseph Proust worked about the composition of elements present in a compound experimentally, he concluded that from any source, a particular compound always contains the same elements in the same proportion by mass/weight.

6. Law of Definite Composition is also known as ________
a) Law of Multiple Proportions
b) Avogadro’s Law
c) Law of Definite Proportion
d) Law of Conservation of Mass

Answer: c
Clarification: Joseph Proust worked about the composition of elements present in a compound experimentally, he concluded that from any source, a particular compound always contains the same elements in the same proportion by mass/weight. Hence it can also be known as the Law of Definite Proportion.

7. The volumes of hydrogen & oxygen when combined bear a simple ratio of 2:1.This is explained by ________
a) Law of Multiple Proportions
b) Avogadro’s Law
c) Law of Definite Proportion
d) Gay Lussac’s Law of Gaseous Volumes

Answer: d
Clarification: When gases combine or as written in a chemical reaction they combine in a simple ratio by volume, provided that all gases are at the same temperature and given pressure, this is called Gay Lussac’s Law of Gaseous Volumes and is proposed by Joseph Louis.

8. Who proposed that equal volumes of all gases at the same temperature & given pressure should contain an equal number of molecules?
a) Antoine Lavoisier
b) Joseph Proust
c) Avogadro
d) Joseph Louis

Answer: c
Clarification: Avogadro’s law is an experimental gas law combining & relating the volume of a gas to the amount of substance of gas present i.e’ directly proportional. This law is valid only for ideal gases. And also only when the pressure and temperature of the given substance are constant.

9. Which of the following is not a law of chemical combination?
a) Law of Multiple Proportions
b) Avogadro’s Law
c) Law of Definite Proportion
d) Law of Conservation of volume

Answer: d
Clarification: Five basic laws are required to govern the combination of elements to form compounds. They are Law of Conservation of Mass, Law of Definite Proportions, Law of Multiple Proportions, Gay Lussac’s Law of Gaseous Volumes, and Avogadro’s Law.

10. Which of the following may be an incorrect statement?
a) Law of Definite Composition is also known as Law of Definite composition
b) Mass can neither be created nor destroyed is Law of Conservation of Volume
c) Antoine Lavoisier conducted many experiments regarding combustion
d) Five basic laws are required to govern the combination of elements to form compounds

Answer: b
Clarification: The correct statement is mass can neither be created nor destroyed is the Law of Conservation of Mass. On conducting many experiments regarding combustion and noticing various physical and chemical changes, there is no change in overall mass hence conservation of mass.

250+ TOP MCQs on Electronic Configurations and Types of Elements: s, p, d and f Blocks and Answers

This set of Chemistry Multiple Choice Questions on “Electronic Configurations and Types of Elements: s, p, d and f Blocks”.

1. Name the element that belongs to s-block but is placed in the p-block.
a) Hydrogen
b) Helium
c) Argon
d) Aluminum
Answer: b
Clarification: Helium’s electronic configuration is 1s2. As the last electron is filled in s-orbital, it belongs to s-block. Since the 1st shell cannot accommodate any orbital than s, 1s2 is completely filled orbital, hence making it, a noble gas. Noble gases are placed in p-block.

2. __________ has both the characteristics of Alkali metals and halogens.
a) Helium
b) Chlorine
c) Sodium
d) Hydrogen
Answer: d
Clarification: As per the outer shell configuration of hydrogen (that is 1s1), it has only one electron in s-orbital making it eligible as an Alkali metal. It requires only 1 electron to obtain a noble gas configuration, which is a characteristic of halogen.

3. ns1 and ns2 are the outer shell configurations of elements in s-block.
a) True
b) False
Answer: a
Clarification: Yes, ns1 and ns2 are the outer shell configurations of elements in s-block. The reason behind this is that they are ready to lose 1 electron or 2 electrons depending on the group number and have low ionization enthalpies.

4. The p-block elements along with s-block elements are called as ________ elements.
a) Inner transition
b) Representative
c) Radioactive
d) Transition
Answer: b
Clarification: The p-block elements comprise of elements from group-13 to group-18 while s-block elements are 1st and 2nd groups. They two together form “Representative elements” or “Main group elements”.

5. What happens to the non-metallic nature as we move from left to right in groups?
a) Increases
b) Decreases
c) Remains constant
d) Irregular
Answer: a
Clarification: Non-metallic nature is defined as a tendency to gain electrons thus having high negative electron gain enthalpies, but the 18th group has no reactivity. So the non-metallic nature increases from left to right in groups leaving noble gases.

6. The outer shell electronic configuration of transition block elements is given by ________
a) (n-1)d1-10ns2
b) (n-1)d1-10(n-1)s0-2
c) (n-1)d1-10ns0-2
d) nd1-10ns0-2
Answer: c
Clarification: Transition block elemts are d-block elements. The electrons fill in the d-orbital, and s-orbital orbital gets varied for maintaing stability of atoms. Therefore the outer shell electronic configuration of transition block elements is given by (n-1)d1-10ns0-2.

7. Which of the following is not true about transuranium elements?
a) Atomic number > 92
b) Elements after Uranium
c) Decay radioactively as they are unstable
d) Example is Thorium
Answer: d
Clarification: The elements after Uranium (Z = 92) are known as transuranium elements, they are unstable and decay radioactively into other elements. But the atomic number of Thorium is 90, hence it is not a transuranium element.

8. Chalcogens are the elements of Group ___________
a) 18
b) 16
c) 12
d) 2
Answer: b
Clarification: Group 16 consists of elements that belong to chalcogens also known as the oxygen family. The elements of this group are oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and Polonium (Po). They are called so because they are mostly found in earth’s crust.

9. Which of the following is not a Metalloid?
a) Germanium
b) Silicon
c) Aluminum
d) Tellurium
Answer: c
Clarification: Metalloids are those with both the properties of metals and non-metals. They are also known as Semi-metals. They are 8 metalloids known till date, namely boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te), polonium (Po) and astatine (At).

10. Metals consist of ______% of the elements known.
a) 78
b) 32
c) 22
d) 68
Answer: a
Clarification: Elements are classified into metals, non-metals, and metalloids based on their properties. While 78% of the elements that are known today are metals. Metallic nature is prominent on the left side of the periodic table.

250+ TOP MCQs on Thermodynamics – Enthalpy Change, ∆rH of a Reaction – Reaction Enthalpy and Answers

Chemistry Question Paper on “Thermodynamics – Enthalpy Change, ∆rH of a Reaction – Reaction Enthalpy”.

1. The standard state of a substance is considered when the temperature is 298 k and the pressure is ____________
a) 1 ATM
b) 1 bar
c) 1 Pascal
d) 760 mm HG
Answer: b
Clarification: All the standard states of a substance are considered when the temperature is 298 Kelvin and the pressure is 1 bar. 1 bar = 0.987 atmospheric pressure = 10000 Pascal = 750.0617 mm of Mercury.

2. All the enthalpies of fusion are positive.
a) true
b) false
Answer: a
Clarification: Fusion is a process of conversion of liquid to solid the enthalpy is energy that is required for a process. As the melting of a solid is endothermic, the enthalpies of fusion are positive so the above statement is true.

3. Consider that, a ball is immersed in water at room temperature and then taken out having 18 grams of water on it, how much amount of energy is required to dry that water at room temperature?
a) 41.43 KJ/mol
b) 49.53 KJ/mol
c) 41.3 KJ/mol
d) 41.53 KJ/mol
Answer: d
Clarification: Heat required to eliminate water : n x ΔvapH = (1 mol) × (44.01 kJ mol–1) = 44.01 kJ mol-1. Δvapor = ΔvapH – ΔnRT = 44.01 kJ mol-1 – 1×8.314 J/K-mol x 298 k x 10-3 = 41.53 KJ/mol. So the amount of energy needed is 41.53 KJ/mol.

4. Calculate the internal energy change when 2 moles of water at 0 degrees converts into ice at 0-degree centigrade?
a) 12 KJ per mole
b) 6 KJ per mole
c) 1 KJ per mole
d) 102 KJ per mole
Answer: a
Clarification: Energy change when 1 mol of water at 0-degree centigrade changes into ice at 0 degrees in centigrade is 6 kJ/mol, So the internal energy change when 2 moles of water at 0 degrees converts into ice at 0 degrees is 12 kJ/mole.

5. What is a change in energy if 18 grams of water is heated from room temperature to 20 degrees above it?
a) 1.50 KJ
b) 0.506 KJ
c) 1.06 KJ
d) 1.506 KJ
Answer: d
Clarification: We know that Q = msΔT, where Q is the energy,m is the mass of water, s is the specific heat of water and T is the temperature. So the change in energy required here = 18 g x 4.184 J/g-K x 20K = 1.506KJ.

6. When a chemical reaction is reversed the value of enthalpy is reversed in sign.
a) true
b) false
Answer: a
Clarification: For example, the formation of ammonia has an enthalpy of -91.8 KJ per mole and the decomposition of ammonia has an enthalpy of + 91.8 KJ per Mol. So the above statement that when a chemical reaction is reversed the value of enthalpy is reversed in the sign is true.

7. Consider the equation 2 H2 + O2 → 2 H2O, what does the 2 in the coefficient of H2O molecule represent?
a) number of particles
b) the number of molecules
c) number of moles
d) number of atoms
Answer: c
Clarification: In a balanced thermochemical equation, the coefficients always refer to the number of the moles (but never molecules) of reactants and products involved in a reaction so 2 in the coefficient of H2O refers to the number of the moles of water.

8. What is the unit of standard enthalpy of fusion or molar enthalpy of fusion?
a) KJ Mol
b) KJ per Mol
c) Mol per KJ
d) 1/KJ Mol
Answer: b
Clarification: The enthalpy change that occurs during melting of one mole of a solid substance in the standard state is called standard enthalpy of fusion or molar enthalpy of fusion, it is represented by the symbol ΔfusH, the units of this are KJ per Mol.

9. Which of the following is not an application of Hess’s law?
a) determination of heat of formation
b) determination of heat of transition
c) determination of Gibb’s energy
d) determination of heat of hydration
Answer: c
Clarification: The following are the applications of Hess’s law; determination of heat of formation, determination of heat of transition and determination of heat of hydration, also to calculate bond energies.

10. ΔHr = Σ ΔHf[products] – Σ ΔHf[reactants].
a) true
b) false
Answer: a
Clarification: The equation ΔHr = Σ ΔHf[products] – Σ ΔHf[reactants] says that the enthalpy of a reaction is the difference between the enthalpy of products and enthalpy of reactants. The above statement regarding enthalpy is true.

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250+ TOP MCQs on Classical Idea of Redox Reactions-Oxidation and Reduction Reactions and Answers

Chemistry Multiple Choice Questions on “Classical Idea of Redox Reactions-Oxidation and Reduction Reactions”.

1. In the reaction of formation of magnesium oxide magnesium undergoes ________
a) reduction
b) oxidation
c) hydrogenation
d) decomposition
Answer: b
Clarification: Oxidation is a process that involves the addition of oxygen to an element or compound or the removal of hydrogen from a compound, an example is of this is the formation of magnesium oxide from magnesium.

2. A zinc ion is formed due to oxidation.
a) true
b) false
Answer: a
Clarification: Oxidation is the loss of electrons by an atom, ion or molecule. it is also known as deelectronation. Zn → Zn2+ + 2e, the loss of electrons from zinc i.e. formation of zinc is an example of oxidation.

3. Removal of oxygen from a compound is an example of ________
a) oxidation
b) reduction
c) oxygenation
d) dehydrogenation
Answer: b
Clarification: Reduction is a chemical process, which involves the addition of hydrogen or an element or compound for the removal of oxygen from a compound. An example of reduction is a chemical reaction;
H2 + F2 → 2HF.

4. Reduction involves in __________ oxidation number.
a) decrease
b) increase
c) independence
d) remain constant
Answer: a
Clarification: The oxidation number is recharged in which an atom appears to have when all the atoms are removed from it as ions. It may have +ve or -ve sign. Reduction results in a decrease in the oxidation number.

5. Formation of copper from copper iron is an example of a reduction.
a) true
b) false
Answer: a
Clarification: Reduction is the gain of electrons by an atom, ion or molecule this process is known as electronation. Prayer for the formation of copper from copper iron as an example of reduction reaction because the copper gains two electrons in this case.

6. Oxidation is the same as __________
a) addition of hydrogen
b) removal of oxygen
c) addition of oxygen
d) removal of Nitrogen
Answer: c
Clarification: Oxidation is the same as the addition of oxygen or removal of hydrogen where reduction is the addition of hydrogen or removal of oxygen. Oxidation is caused by an oxidising agent and reduction is caused by a reducing agent.

7. Formation of zinc sulphide is an example of ___________
a) reduction
b) oxidation
c) removal of oxygen
d) addition of hydrogen
Answer: b
Clarification: Addition of electronegative element or removal of any other electropositive element is also considered as a process that involves oxidation. Here, sulphur is an electronegative element. So the formation of zinc sulphide is an Oxidation reaction.

8. SnCl2 + 2FeCl2 → SnCl4 + 2FeCl2 is an example of __________________ reaction.
a) only oxidation
b) only reduction
c) redox
d) neither oxidation nor reduction
Answer: c
Clarification: Chemical reactions which involves both oxygen as well as reduction process simultaneously are known as redox reactions. The above given reaction involves both oxidation and reduction reactions, so it is a Redox reaction.

9. SnCl2 + 2FeCl2 → SnCl4 + 2FeCl2. Which of the following element undergoes oxidation in the reaction given?
a) iron
b) tin
c) chlorine
d) ferrous
Answer: b
Clarification: Tin changes is oxidation state from + 2 to + 4. Increase in oxidation number indicates Oxidation reaction. Oxidation is the loss of electrons by an atom, ion or molecule, it is also known as the deelectronation.

10. Which of the following do you think is a correct statement?
a) oxidation is caused by a reducing agent
b) the oxidation reaction is a Redox reaction
c) addition of electropositive element is a type of oxidation
d) reduction is the addition of hydrogen
Answer: d
Clarification: Oxidation is caused by an oxidizing agent, both oxidation and reduction reaction is combined together to form a Redox reaction and the addition of electropositive element is a type of reduction so the correct statement is that reduction as the addition of hydrogen.

250+ TOP MCQs on s-Block Elements – Important Compounds of Calcium and Answers

Chemistry Multiple Choice Questions on “s-Block Elements – Important Compounds of Calcium”.

1. Which of the following acid chemical formula first slaked lime?
a) Calcium chloride
b) Calcium oxide
c) Calcium hydroxide
d) Calcium carbonate
Answer: c
Clarification: When 1 mole of burnt lime, that is calcium oxide is combined with 1 mole of the hydrogen molecule, a hissing sound appears and slaked lime is produced along with the heat. The chemical formula for slaked lime Ca(OH)2.

2. Quicklime as same as calcium oxide.
a) True
b) False
Answer: a
Clarification: Yes, calcium oxide chemical formula is CaO and it is also called as quicklime or simply lime. It is prepared by the thermal decomposition of calcium carbonate at 1072-1270 Kelvin, carbon dioxide comes as a byproduct and it is a basic oxide.

3. Which of the following is not a compound of mortar?
a) Phenol
b) Quicklime
c) Sand
d) Water
Answer: a
Clarification: Quicklime or calcium oxide (CaO) is used as a basic flux, for removing the hardness of water, also used in mortar. A mixture of quick lime and sand in the ratio 1:3 with enough water to make a thick place is called motor.

4. What is the enthalpy of heat for dissolving quicklime and water?
a) 55 kJ/mol
b) 63 kJ/mol
c) 75 kJ/mol
d) 78 kJ/mol
Answer: b
Clarification: Calcium hydroxide is prepared by dissolving quicklime and water and the enthalpy change for this reaction is 63 kJ/mole (the sign is negative). Here the chemical formulae for quicklime and Calcium hydroxide are CaO and Ca(OH)2 has twice respectively.

5. Which of the following compound is formed when slaked lime is treated with excess dioxide in the presence of water?
a) Barium sulphate
b) Calcium carbonate
c) Calcium hydroxide
d) Calcium bicarbonate
Answer: d
Clarification: When 1 mole of Calcium Hydroxide is treated with an excess of carbon dioxide in the presence of water, it results in the formation of calcium bicarbonate which is soluble. It is one of the most important properties of slaked lime.

6. Limestone is insoluble in water.
a) True
b) False
Answer: a
Clarification: Calcium carbonate is also known as limestone or marble are chalk, its chemical formula is given by CaCO3. It is insoluble in water but dissolves in the presence of carbon dioxide due to the formation of calcium bicarbonate.

7. Can limestone be prepared through slaked lime?
a) Yes
b) No
c) Maybe
d) Cannot say
Answer: a
Clarification: Yes, limestone can be prepared through slaked lime. Limestone is calcium carbonate while slaked lime is calcium hydroxide. When limestone is passed through carbon dioxide, it results in the formation of calcium carbonate which is a precipitate and water.

8. Which of the following do you think is the correct formula for gypsum?
a) CaSO4.2H2O
b) CaSO4.1/2H2O
c) CaSO4.H2O
d) CaSO4
Answer: a
Clarification: Gypsum is a compound of calcium. It is chemically calcium sulphate dehydrate and it is also known as alabaster. It is added to cement to slow down at speed of setting. It’s really very essential in our day to day life.

9. Gypsum is the same as plaster of Paris.
a) True
b) False
Answer: b
Clarification: Plaster of Paris is calcium sulphate hemihydrate and gypsum is calcium sulphate dihydrate. On heating gypsum at 390 Kelvin, it gives plaster of Paris. The chemical formula of gypsum and plaster of Paris is CaSO4.2H2O and CaSO4.1/2H2O respectively.

10. What is dead burnt plaster?
a) Hexahydrate calcium sulphate
b) Hemihydrate calcium sulphate
c) Anhydrous calcium sulphate
d) Decahydrate calcium sulphate
Answer: c
Clarification: When plaster of Paris or calcium sulphate hemihydrate, which is given by the chemical formula CaSO4.1/2H2O is heated about 393 Kelvin, no water of crystallization is left and anhydrous calcium sulphate is formed, it is known as dead burnt plaster.

11. Is the plaster of Paris useful in setting a solid mass?
a) Yes
b) No
c) Maybe
d) Cannot say
Answer: a
Clarification: When plaster of Paris or calcium sulphate hemihydrate which is given by the chemical formula CaSO4.1/2H2O is mixed with water, it forms of plastic mass which sets into a solid mass with slight expansion due to dehydration and its reverse conversion into gypsum.

12. What is chloride of lime?
a) Calcium sulphate
b) Calcium chloro hypochlorite
c) Calcium chloride
d) Calcium hydroxide
Answer: b
Clarification: Chloride of lime is chemically known as calcium chloro hypochlorite and it is given by the chemical formula CaOCl2, it is also known as bleaching powder. Bleaching powder is prepared by the fusion of calcium hydroxide and chlorine.

13. What is the average percentage of available chlorine theoretically?
a) 85
b) 49
c) 58
d) 66
Answer: b
Clarification: With an excess of dilute sulfuric acid and carbon dioxide, calcium chloro hypochlorite forms chlorine, which is known as available chlorine. The average percentage of available chlorine is 35 to 40% but theoretically, it should be 49%, which diminishes on keeping the Powder due to a chemical change.

14. Which of the following is not a use of calcium chloro hypochlorite?
a) Sterilization of water
b) Manufacture of chloroform
c) Germicide
d) Painting
Answer: d
Clarification: Calcium chloro hypochlorite or chloride of lime or bleaching powder which is chemically CaOCl2 is used for bleaching, as a disinfectant and germicide in the sterilization of water, for making wool which is unshrinkable and in the manufacture of chloroform.

15. In the average composition of portland cement, the percentage of magnesium oxide is a ___________
a) 3 to 4%
b) 2 to 3%
c) 4 to 5%
d) 1 to 2%
Answer: b
Clarification: Cement is an important building material. The average composition of portland cement is calcium oxide of 50 to 60%, Silicon dioxide of 20 to 25%, aluminium oxide of 5 to 10%, magnesium oxide of 2 to 3%, ferric oxide of 1 to 2% and sulphur trioxide of 1 to 2%.

250+ TOP Hydrocarbons – Alkanes MCQs and Answers Quiz

Chemistry Multiple Choice Questions on “Hydrocarbons – Alkanes”.

1. Alkanes are also known as __________
a) alkenes
b) paraffin
c) aromatic
d) alicyclic

Answer: b
Clarification: Alkanes are saturated aliphatic open chain hydrocarbons with carbon-carbon single bonds. They are inert under normal conditions they do not react with acids, bases and other reagents. They were earlier known as paraffin, in Latin Param = little and affine means affinity.

2. Is of hydrogenation is __________ on steric crowding.
a) may be related to
b) dependent
c) independent
d) not related to

Answer: b
Clarification: Ease of hydrogenation depends on the steric crowding across multiple Bond, more the steric crowding, the less is reactivity towards hydrogenation. This concept is used in one of the methods of preparation of alkanes from the hydrogenation of alkenes and alkynes.

3. How many carbons are there in the product of a decarboxylation reaction when compared with the reactant?
a) two carbons more
b) one carbon more
c) one carbon less
d) an equal number of carbons

Answer: c
Clarification: Decarboxylation of sodium or potassium salt of fatty acids is decarboxylation reaction. This reaction is used for descending of series as the alkane obtained has one carbon less than the parent compound. Here quicklime is used as it is more hygroscopic than sodium hydroxide and keeps Sodium Hydroxide in a dry state.

4. Which of the following reaction is used to increase the length of the carbon chain?
a) Wolff Kishnn’s reaction
b) Clemmensen reduction
c) Kolbe’s electrolysis
d) Wurtz reaction

Answer: d
Clarification: Wurtz reaction is used to increase the length of the carbon chain, Kolbe’s electrolysis is used when alkanes require even number of carbon atoms while clemmensen reduction and wolff-kishner are used for removing water molecule.

5. Corey-House synthesis is used for alkanes having __________ number of carbon atoms.
a) 6
b) 3
c) 2
d) 4

Answer: b
Clarification: Corey-House synthesis is one of the methods of preparation of alkanes and this method can be used to prepare alkanes having an odd number of carbon atoms. As 6, 2, and 4 are even numbers only the compound with three carbon atoms can be prepared.

6. Alkynes are __________ in nature and first four members are __________ gases.
a) polar, white
b) nonpolar, colourless
c) polar, colourless
d) nonpolar, white

Answer: b
Clarification: Alkanes being nonpolar in nature, soluble in nonpolar solvents but insoluble and polar solvent such as water. The first four members of alkanes are colourless gases, the next 13 members are colourless liquids and next higher members are colourless solids, this can be explained on the basis of the magnitude of attraction forces.

7. Which of the following is not a process of halogenation of alkanes?
a) acylation
b) chlorination
c) bromination
d) iodination

Answer: a
Clarification: Chlorination, bromination and iodination are the processes of halogenation of alkanes. Mechanism of halogenation of alkanes is free radical in nature that is the attacking reagent is a halogen-free radical, therefore it is a chain reaction.

8. In the combustion reaction of alkanes if Ethane is used how many moles of oxygen are required?
a) 3
b) 4
c) 7
d) 3.5

Answer: d
Clarification: The combustion reaction of alkanes has a standard reaction that is CnH2n+2 + (3n/2 + 1/2)O2 → nCO2 + (n + 1)H2O. In the case of combustion of ethane, n = 2. That means the number of moles of oxygen required is 3(2)/2 + 1/2 = 3.5

9. Methane cannot be prepared by the reduction of alkenes or alkynes.
a) true
b) false

Answer: a
Clarification: Methane cannot be prepared by reduction of alkenes or alkynes because alkanes or alkynes require a minimum of two carbon atoms in order to form, but Methane has only a single carbon in it Methane cannot be prepared by Kolbe’s electrolysis and woods reaction also.

10. Which of the following is true regarding the boiling point?
a) cannot say
b) n-Octane is greater than isooctane
c) n-Octane is less than isooctane
d) n-Octane is equal to isooctane

Answer: b
Clarification: The boiling point of alkanes decreases on branching and boiling point is directly proportional to the van der walls forces and the van der wall forces are directly proportional to the molecular mass as well as surface area. So we can say that the boiling point of n-Octane is greater than that of isooctane.