Category: Class 11 Chemistry Objective Questions

Chemistry MCQs for Class 11 on “Thermodynamics – Spontaneity”.

1. Which of the following is not a spontaneous process?
a) sugar dissolves in water
b) melting of iron
c) rusting of iron
d) evaporation of water
Answer: b
Clarification: A physical or chemical process which occurs by its on in a particular direction under a particular set of conditions without any force is known as a spontaneous process and it cannot be reversed. Here melting of iron is only possible when we supply a large amount of heat so it is not a spontaneous process.

2. Spontaneous reactions that occur or mostly ________in nature.
a) endothermic
b) exothermic
c) both endothermic and exothermic
d) neither exothermic nor endothermic
Answer: b
Clarification: All the processes which occur with a decrease of energy are exothermic in nature, those with change of enthalpy as negative occurs spontaneously. It is not true in case of some endothermic reactions, when they occur spontaneously.

3. Entropy increases for a spontaneous reaction.
a) true
b) false
Answer: a
Clarification: A process is spontaneous if and only if the entropy of Universe increases for a process to be spontaneous ΔS(universe) > 0. At equilibrium, ΔS = 0. Saudi about the statement that the Entropy increase for a spontaneous reaction is true.

4. Entropy is an ___________ property.
a) intensive
b) extensive
c) neither intensive or extensive
d) both intensive and extensive
Answer: b
Clarification: Entropy is a measurement of randomness or disorder of molecules it is a state function as well as an extensive property. Its units are J/K-mole. Extensive property depends on the size and quantity of the mass.

5. Which of the following relation is true between Gibbs energy, enthalpy, temperature, and entropy?
a) G = H -TS
b) G = H -T
c) G = H -S
d) G = -TS
Answer: a
Clarification: The energy that is available for a system at some conditions and by which useful work can be done is Gibbs free energy. The relation between Gibbs free energy, enthalpy, temperature and entropy is given by Gibbs Helmholtz equation; G = H -TS.

6. Reaction is spontaneous if Gibbs free energy is __________
a) greater than zero
b) equal to zero
c) less than zero
d) infinity
Answer: c
Clarification: A reaction is spontaneous if Gibbs free energy is less than zero and the reaction is nonspontaneous if the Gibbs free energy is greater than zero. The reaction is at equilibrium state if gives free energy is equal to zero.

7. If the enthalpy is positive and entropy is negative, what do you understand about Gibbs free energy?
a) it is positive
b) negative
c) may be negative
d) may be positive
Answer: a
Clarification: According to the Helmholtz equation; G = H -TS, when enthalpy H is positive and entropy S is negative, the Gibbs free energy is always positive and the reaction is not spontaneous at all temperatures.

8. The entropy of the universe is always increasing is ____________
a) zeroth law of thermodynamics
b) first law of thermodynamics
c) second law of thermodynamics
d) third law of thermodynamics
Answer: b
Clarification: The second law of thermodynamics is given as the entropy of the universe is always increasing in the course of every spontaneous or natural change also can be said as the heat cannot flow itself from a colder to a hotter body.

9. Third law of thermodynamics is only applicable for perfectly crystalline substances.
a) true
b) false
Answer: a
Clarification: We can define the third law of thermodynamics entropy of a perfectly crystalline substance at zero kelvin or absolute zero is taken to be zero, but this is not applicable if there is any Imperfection at 0 k, the entropy will be larger than 0.

10. ΔS(universe) > 0 can also be written as _________
a) ΔS(system) + ΔS(surroundings) > 0
b) ΔS(surroundings) > 0
c) ΔS(system)
d) ΔS(system) – ΔS(surroundings) > 0
Answer: a
Clarification: ΔS(universe) > 0 can also be written as ΔS(system) + ΔS(surroundings) > 0, as the universe is nothing but the system and surroundings. The above mentioned condition is used when a reaction is at equilibrium.

To practice Chemistry MCQs for Class 11,

Chemistry Online Quiz for Class 11 on “Redox Reactions – Oxidation Number”.

1. Can 1/2 be an oxidation number?
a) yes
b) no
c) may be
d) cannot say
Answer: a
Clarification: The oxidation number is defined as the change in which appears to have when all other atoms are removed from it as ions it can be a whole number or a fractional or 0. So 1/2 can be an oxidation number.

2. The oxidation number of oxygen in Ozone is 1, -1 and 0.
a) true
b) false
Answer: a
Clarification: An element may have different values of oxidation number depending upon the nature of the compound in which it is present. Ozone molecule has three oxygens and the oxidation numbers of them are 1, – 1 and 0.

3. Helium element has an Oxidation state of ____________
a) 2
b) 0
c) 1
d) -1
Answer: b
Clarification: All elements in the elementary state have an oxidation number of zero. So helium element also has an Oxidation state of zero. It is one of the most important points for determining the oxidation number.

4. In NaH, the oxidation state of hydrogen is _______________
a) 2
b) 1
c) -1
d) 0
Answer: c
Clarification: In all compounds except ionic metal hydride the oxidation number of hydrogen is +1. But in metal hydrides like sodium hydride, magnesium hydride, calcium hydride, etc, the oxidation number of hydrogen as -1.

5. What is the oxidation state of Cr in CrO₅?
a) 3
b) 4
c) 5
d) 6
Answer: d
Clarification: The oxidation states of oxygens in CrO₅ are -1, -1, -1, -1 and -2. The oxidation state of Cr is given by x. Therefore x + 4(-1) + (-2)(1) = 0. X = 6. The oxidation state of chromium in chromium peroxide is 6.

6. What is the oxidation state of C in C₃O₂?
a) 0
b) 2
c) -2
d) 0, 2, 2
Answer: d
Clarification: The structure of C₃O₂ is given as O=C=C=C=O. Where the oxidation number of carbon beside oxygen is +2 due to oxygen’s -2 oxidation state. And the middle carbon’s oxidation is 0, due to +2 charge on it’s both sides.

7. What is the oxidation state of N in NH₄NO₃ (in order)?
a) -3, 5
b) 5, -3
c) 5
d) -3
Answer: a
Clarification: Dividing into two parts oxidation number of N in NH₄⁺ is x; x + 4*1 = +1; x = -3, oxidation number of N in NO₃^– is y; y + 3*-2 = -1; y = 5. The oxidation States of Nitrogen in this compound are -3 and 5 respectively.

8. What is the average oxidation state of S in Na₂S₆O₆?
a) 5
b) 0
c) 5/2
d) 2
Answer: c
Clarification: the average Oxidation state of elements in a compound is the average of the different oxidation States. The average oxidation state of S in Na₂S₆O₆ is x. 2(1) + 4x + 6(-2) = 0; x = 5/2. The average Oxidation state of sulfur here is 5/2.

9. What is the stock notation of cuprous oxide?
a) copper oxide
b) copper (I) oxide
c) copper 1 oxide
d) copper 2 oxide
Answer: b
Clarification: The elements exhibiting different Oxidation States i.e. are denoted by Roman numeral such as I, II, III, IV etc, within parenthesis after the symbol or name of the element this is known as stock notation.

10. What is the stock notation of mercuric chloride?
a) Mercury
b) Mercuric chloride
c) Chloride
d) Mercury (II) chloride
Answer: d
Clarification: The system that exhibits variable oxidation States in specified Roman numerals within parentheses after the symbol is the name of the element is known as stock notation. Mercury (II) chloride is in stock notation.

To practice Chemistry Online Quiz for Class 11,

Chemistry Multiple Choice Questions for NEET Exam on “p-Block Elements – Important Trends and Anomalous Properties of Boron”.

1. Group 13 hydrides are formed directly.
a) true
b) false
Answer: b
Clarification: Elements of group 13 do not combine directly with hydrogen to form hydrides, therefore their hydrides have been prepared by indirect methods. An example is that diborane is formed when Boron fluoride is combined with lithium aluminium hydride in the presence of dry Ether.

2. All the oxides and hydroxides of Boron family are ____________ in nature.
a) acidic
b) basic
c) acidic and basic
d) acidic, basic and amphoteric
Answer: d
Clarification: On moving top to bottom of the group, there is a change from acidic to amphoteric and then to basic character, of oxides and hydroxides of group 13 elements. Only boric acid is soluble in water while the other hydroxides are insoluble in water.

3. Which of the following is a colourless gas?
a) Boron chloride
b) Boron fluoride
c) Boron Bromide
d) Boron iodide
Answer: b
Clarification: All the halides of Boron are trihalides, boron chloride is a colourless fuming liquid, boron fluoride is a colourless gas, boron bromide is a colourless fuming liquid and Boron iodide is a white solid at room temperature, all these trihalides of boron are lewis acids.

4. Which of the following is true regarding the acidic character?
a) Aluminium halides acidic character is greater than that of indium halide
b) Boron halide acidic character is less than that of gallium halide
c) Gallium halides acidic character is less than that of indium halide
d) Aluminium halides acidic character is greater than that of boron halide
Answer: a
Clarification: The halides of group 13 elements behave as lewis acids. The correct order of their acidic character decreases from boron, aluminium, gallium and indium. Here halide refers to chlorine, bromine and iodine whereas thallium trichloride can act only as an oxidising agent as it decomposes easily.

5. Which of the following compound is formed when aluminium reacts with an alkali?
a) sodium Tetra hydroxyl aluminate V
b) sodium Tetra hydroxyl aluminate III
c) sodium Penta hydroxyl aluminate IV
d) sodium Septa hydroxyl aluminate III
Answer: b
Clarification: When two moles of aluminium atom is combined with two moles of sodium hydroxide in presence of 6 moles of water, two moles of sodium tetra hydroxyl aluminate III is formed along with three moles of the hydrogen molecule.

6. Which of the following element has the highest melting point?
a) thallium
b) gallium
c) aluminium
d) boron
Answer: d
Clarification: Boron has a very high melting point when compared to the other elements in group 13, this is because of its three-dimensional structure in which boron atoms are held together by strong covalent bonds, it also has a higher boiling point comparatively.

7. ____________ and Boron are same in case when reacted with concentrated nitric acid.
a) Oxygen
b) Aluminium
c) Hydrogen
d) No other metal
Answer: d
Clarification: Boron can be oxidized by concentrated nitric acid, while aluminium becomes passive due to the formation of an oxide layer on the surface. Boron combines with nitric acid in order to produce boric acid and nitrous oxide.

8. Which of the following is the correct reason for the anomalous behaviour of Boron?
a) low ionization energy
b) smallest size in the group
c) low electronegativity
d) the presence of the orbital and can show allotropy
Answer: b
Clarification: Boron shows anomalous behaviour with the other members of the group because of the smallest size and the group, highest ionization energy, highest electronegativity in the group, absence of vacant d- orbital and the allotropy, while the other members do not show.

9. Boron shows a diagonal relationship with ____________
a) thallium
b) lithium
c) magnesium
d) aluminium
Answer: a
Clarification: There is a diagonal relationship between boron of group 13 and silicon of group 14 as they resemble each other like Lithium of group 1 and magnesium of group 2. There are many characteristics which resemble both boron and silicon.

10. Do Boron and silicon react with electropositive metals?
a) Yes
b) No
c) Maybe
d) May not be
Answer: a
Clarification: Both boron and silicon form covalent hydrides like boranes and silanes respectively. They do react with electropositive metals and give binary compounds, which yield a mixture of boranes and silanes on hydrolysis.

11. Which of the following property is not a similarity between Boron and silicon?
a) metals
b) non-metals metals
c) semiconductors
d) formation of covalent hydrides
Answer: a
Clarification: Boron of group 13 and silicon of group 14 share a diagonal relationship and have many similarities. Both boron and silicon are non-metals, semiconductors and they also form covalent hydrides, therefore, they are not metals.

12. Boron and silicon form covalent and volatile halides.
a) true
b) false
Answer: a
Clarification: Both boron of group 13 and silicon of group 14 form covalent and volatile halides, which fume in moisture air due to the release of HCl gas. They react with water in order to form boric acid and silicon hydroxide along with hydrochloric gas which is volatile in nature.

13. ____________ Boron is reactive with air.
a) Neither crystalline nor amorphous
b) Crystalline
c) Both crystalline and amorphous
d) Amorphous
Answer: d
Clarification: Crystalline Boron is unreactive whereas amorphous Boron is reactive. It reacts with air at 700-degree centigrade, boron combines with oxygen and nitrogen separately to form its oxide and nitride.

14. Which of the following elements do you think can react with water?
a) Thallium
b) Boron
c) Aluminium
d) Gallium
Answer: a
Clarification: Both boron and aluminium do not react with water but amalgamated aluminium reacts with water and evolves hydrogen. Gallium and indium do not react with cold or hot water but thallium forms an oxide layer on the surface.

15. Which of the following elements is more reactive with air?
a) indium
b) gallium
c) thallium
d) all three are equally reactive
Answer: c
Clarification: Thallium is more reactive with their than gallium and indium, due to the formation of unipositive ion Tl⁺. Thallium combines with oxygen in the air in order to form thallium oxide, Tl₂O is more stable than Tl₂O₃ due to inert pair effect.

To practice Chemistry Multiple Choice Questions for NEET Exam,

Chemistry Online Quiz for NEET Exam on “Hydrocarbons – Alkynes”.

1. What is a general formula of alkynes?
a) C_nH_2n-2
b) C_nH_n-2
c) C_nH_2n
d) C_nH_2n+2
Answer: a
Clarification: Alkynes are unsaturated hydrocarbons with the general formula of C_nH_2n-2. Few examples are ethyne (put n = 2 in the general formula) C₂H₂, propyne (put n = 3 in the general formula) C₃H₄, butyne (put n = 4 in the general formula) C₄H₆ etc.

2. Are alkynes more reactive than alkenes?
a) Yes
b) No
c) Cannot say
d) Maybe
Answer: b
Clarification: The alkynes exhibit electrophilic addition reaction, they are less reactive when compared with alkenes and this is due to the dissociation of π-electron cloud requires more energy comparatively. So we can say that they are not more reactive when compared to alkenes.

3. Alkynes can be prepared from calcium carbide.
a) true
b) false
Answer: a
Clarification: Calcium carbonate is heated and results in the formation of calcium oxide and carbon dioxide and then calcium oxide combines with carbon in order to form calcium carbide and carbon monoxide, when calcium carbide combines with water it forms calcium hydroxide as well as an alkyne that is Ethyne C₂H₂.

4. All alkynes are odourless gases.
a) true
b) false
Answer: b
Clarification: The first two members are gases, the next eight members are liquids and higher members are solids. Alkynes are colourless and odourless with the exception of acetylene, which has slightly garlic or due to the presence of phosphine gas and hydrogen sulphide gas.

5. Alkynes are ________________ in water and the melting point ________________ with increase in molar mass.
a) soluble, decrease
b) insoluble, increase
c) insoluble, decrease
d) soluble, increase
Answer: b
Clarification: Alkynes are insoluble in water but soluble in organic solvents like ethers, carbon tetrachloride and Benzene. The melting point, boiling point and density of alkynes increase with the increase in the molar mass.

6. Alkynes show ________________ reactions.
a) neither electrophilic nor nucleophilic addition
b) nucleophilic addition only
c) electrophilic only
d) both electrophilic and nucleophilic addition
Answer: d
Clarification: Alkynes show electrophilic as well as nucleophilic addition reactions. Electrophilic addition reactions follow the markownikoff rule, various examples for these reactions are the addition of dihydrogen, halogens, water and hydrogen halides.

7. Do alkynes react with arsenic trichloride?
a) Yes
b) No
c) Cannot say
d) Maybe
Answer: a
Clarification: Yes, when ethyne reacts with arsenic trichloride in presence of anhydrous aluminium trichloride, it forms 2 chloro vinyl arsonous dichloride, it is also known as Lewisite, which is a poisonous gas. So we can say that alkynes do react with arsenic trichloride.

8. Ethyne on oxidation with alcoholic KMnO4 forms ________________
a) hydrochloric acid
b) oxalic acid
c) acetic acid
d) formic acid
Answer: b
Clarification: When one mole of ethane reacts with alcoholic KMnO₄ 1 mole of oxalic acid is formed, when it reacts with acidic KMnO₄ two moles of formic acid are formed and when it reacts with K₂Cr₂O₇ one mole of Acetic acid is formed.

9. At which temperature, does cyclic polymerization of an alkyne occur?
a) 871 Kelvin
b) 872 Kelvin
c) 873 Kelvin
d) 874 Kelvin
Answer: c
Clarification: An example of cyclic polymerization of an alkyne is given by; when 3 moles of ethane is at 873 Kelvin in presence of red hot iron tube they polymerise in a cyclic form in order to form Benzene a six-membered ring with alternate double bonds.

10. When ethyne is subjected to ozonolysis of, what is the end product?
a) formic acid
b) acetic acid
c) oxalic acid
d) glucose
Answer: a
Clarification: When a mole of ethane is subjected to ozonolysis, it reacts with a mole of ozone in presence of carbon tetrachloride and zinc or water, in order to give one mole glyoxal and then it forms two moles formic acid.

To practice Chemistry Online Quiz for NEET Exam

Chemistry Multiple Choice Questions on “Mole Concept and Molar Masses”.

1. According to S.I. the system, ______ was used to measure the amount of substance.
a) mole
b) weight machine
c) weight
d) mass
Answer: a
Clarification: One mole is the amount of a substance that contains as many particles as there are atoms in exactly 12 g of the carbon atom. So S.I. the system took mole as the seventh base fundamental quantity (symbol = mol).

2. What’s the number of entities or particles together in mole concept known as?
a) Boltzmann constant
b) Avogadro’s number
c) Universal gas constant
d) Reynold’s number
Answer: b
Clarification: Avogadro number denoted by N_A. Its value is 602213670000000000000000, also written as 6.022×10²³. It’s the number of entities in 1 mol of a substance. The units may be electrons, atoms, ions, or molecules, depending on the nature of the substance.

3. 1 u = M_a/N_A.
a) True
b) False
Answer: a
Clarification: In the above given equation 1 u = M_u/N_A; “u” refers to the atomic mass unit, M_u refers to molar mass constant(Its value is defined to be 1 g/mol in SI units). 1 u = M_a/N_A = 1.660539040 x 10^-27 kg. Hence the above statement is true.

4. A mole of any substance contains _______
a) 6.022 x 10²⁶ particles
b) 6.022 x 10²² particles
c) 6.022 x 10²³ particles
d) 3.022 x 10²² particles
Answer: c
Clarification: The answer is Avogadro’s number. One mole of any substance contains Avogadro’s number of particles. Avogadro number denoted by N_A. Its value is 602213670000000000000000, also written as 6.022×10²³.

5. 12.044 x 10²³ atoms of oxygen contains _______
a) 1 mole of oxygen
b) 2 moles of oxygen
c) 3 moles of oxygen
d) 4 moles of oxygen
Answer: b
Clarification: One mole of any substance contains Avogadro’s number of particles. Its value is 6.022×10²³ atoms. But here it’s given 12.044 x 10²³ atoms, thereby dividing it by Avogadro’s number; 12.044 x 10²³ atoms/6.022×10²³ atoms = 2 moles. Hence it contains 2 moles of oxygen.

6. If one mole of ammonia contains “y” number of particles, then how many particles do 1 mole of glucose contain?
a) 2y
b) 0.5y
c) 3y
d) y
Answer: d
Clarification: Let it be any compound, but one mole of a substance always contains Avogadro’s number of particles. In the above question, Avogadro’s number (6.022×10²³) is given by the letter “y”. so, in 1 mole of glucose, there is y number of particles.

7. What’s the number of particles in 10 moles of hydrochloric acid?
a) 6.022 x 10²² particles
b) 6.022 x 10²³ particles
c) 6.22 x 10²³ particles
d) 3.22 x 10²² particles
Answer: a
Clarification: One mole of any substance contains Avogadro’s number of particles. Its value is 6.022×10²³ atoms. But here the question is about 10 moles of a substance. So multiply the Avogadro’s number by 10. Therefore 6.022×10²³ x 10 = 6.022×10²².

8. Which of the following statement is correct?
a) The value of Avogadro’s number is 6.022×10²² atoms
b) One molecule of any substance contains Avogadro’s number of particles
c) One mole is the amount of a substance that contains as many particles as there are atoms in exactly 12 g of the carbon atom
d) 1 u is not equal to M_a/N_A
Answer: c
Clarification: The corrected statements are as follows: the value of Avogadro’s number is 6.022×10²³ atoms, one molecule of any substance contains Avogadro’s number of particles & 1 u = M_a/N_A. The correct option is that one mole is the amount of a substance that contains as many particles as there are atoms in exactly 12 g of the carbon atom.

9. One mole of sucrose contains how many grams of sucrose?
a) 342g
b) 343g
c) 341g
d) 340g
Answer: a
Clarification: One mole of sucrose is C₁₂H₂₂O₁₁ The individual mass of carbon is 12 amu, the individual mass of hydrogen is 1 amu & the individual mass of oxygen is 16 amu. But sucrose has 12 carbons, 22 hydrogens and 11 oxygens, that is 12 x 12 + 22 x 1 + 11 x 16 = 342g.

10. 1 mole of ammonia is of 17 g. Then what is the mass of 0.3 moles of ammonia?
a) 21g
b) 2.1g
c) 17g
d) 1g
Answer: b
Clarification: Given that, 1 mole of ammonia is of 17 g. 0.3 mole of ammonia contains 17 x 0.3g of mass. IT’s because the molecular weight of a given pcompound is directly proportional to the number of moles of the given compound.